I would think an Ikea Hack or Barn doors would be the cheapest. good luck!

You could put a tension rod across the opening and do curtains instead, if it doesn't conflict with a super-sleek decor.

An architect friend made his sliding closet doors with beautiful rice paper, with lights in the closet which made the doors function as beautiful glowing lamps.

The closet doors in my apartment are sticky and block the doors to the room, so we took them down and did curtains instead. Although, if you've got a toddler, this might not be the way to go, or it's the perfect way to make you keep your closet organized.

As for curtains or rice paper, we used sari fabric from JoAnn's, and I've seen rice paper at IKEA relatively inexpensive (and used it to cover the french doors to my bedroom in my old place!).

What about those ikea sliding panels? I think they can be adjusted to height.

I like the sliding closet doors with rice paper idea - you can fairly inexpensive tracks from Ikea that will carry lightweight doors.
That said I can see a toddler lunging at them and hands going thru the rice paper a bit too easily.
Might i suggest you do clear plexi BACKED with the rice paper or sari or other fabric. In that way they will wipe clean but still look good, and you can do the lighting trick suggested above. A frame made of lightweight wood & reinforced by the plexi sheets would be plenty strong, while still lightweight enough to slide...

Home Depot has shoji-like frosted glass doors with different numbers of panels (3-5) that are very reasonable. We put them in our last condo, and they definitely helped sell the place. The 5-panel doors look almost exactly like the ones pictured. They were very easy to install too.

My husband and I had the same exact problem with closet-doors while renovating our condo. In-fact it was the last project left and needed to get them done quickly because we were going to sell our condo. We had looked into so many different options, but the cheapest thing we found was to make our own. They turned out great and cost us very little. Here are some pictures of the closet-doors before we painted them.

Picture 1

Picture 2

If you need more help or have any questions about how we made these closet doors feel free to contact me through my Blog. Good Luck!

Oh, and we had a toddler.

i would go with old doors from a junkyard/salvage or CL.

This is the brand of doors that Jillofalltrades is talking about. Unfortunately, I think they either discontinued the dark wood ones with frosted glass or don't have them online anymore. Ask in the store, though...here are the plain white ones.

http://www.homedepot.com/Doors-Windows-Doors-Interior-Doors/h_d1/N-5yc1vZ1xhcZar1h/R-100495422/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

I considered these for our house too...but we may just go with an inexpensive tension rod/grommet curtain setup for now.

Try Craigslist--french doors come up on there sometimes for a really good price.

I removed my closet doors and installed curtains. Ikea's KVARTAL system is very cool as it can be suspended from the ceiling and wrapped around corners seamlessly. Plus it's super cheap. I did the whole thing for around $65 - including the drapes!

I installed these and continued them around a corner so it became a feature of the room and not just "curtains where door was". It looks very modern without being cold or harsh.

However, if you're going for resale, I would do the Barn Doors. They look cool, are sturdy and an interesting feature. Shoji screens are neat too, but if you have kids, a cat, or "topple-prone" closets, the rice paper is in jeopardy and once it tears, there's no going back.

One of the things you need to be careful with especially since you have a young child is to make sure you have a sliding track on the floor. Barn doors or sliding doors only top mounted can pop off if one is to lean or put pressure on them and is especially dangerous if you live in earth quake land. So I recommend top and bottom track.

I have saved this image because I love the look of the doors and some other elements. You could install a flat plain surface and wallcover them -
http://www.flickr.com/photos/44713708@N00/3279549474/in/set-72157622103111178/

If you want an integrated look, simple slab doors on a track can look clean. And since they're hollow are easy to mount. Any lumber store should carry them (or can order them for you).

Solid wood doors are expensive. I recently found nice solid molded mdf doors at Trustile:

www.trustile.com

We have used curtains for ours, in lieu of sliders. Works well for a closet, but not so well for pocket door for dividing rooms up.

If you want sliders, get the hardware from McMaster-Carr, it'll run you about $200-$300 if my memory is correct. Pick up some used doors from Builders Resources off Third St. We've picked up several from there for various projects, including a wonderful glass back door for around $50.

You'd be surprised at how easy it is to build shoji-type doors inexpensively from basic materials, I'd recommend searching a bookseller's site or your local library for a book, one friend built them and then added a super lightweight plexi (patience yielded them leftover cuts for cheaper) for more privacy, they simply inserted a miniature quarter round shoe molding on the inside to hold in the plexi. I believe they said it cost about $30 to make each door so guess who I'm going to bribe to come over and build my new pantry doors?!

You might try salvage places like Urban Ore and Omega Salvage in Berkeley--they have all kinds of vintage doors there and very well could have something that would work for you.

I can't believe so many people are suggesting rice paper with a toddler... I'D break rice paper, so I think a two-year-old would definitely fall through at some point!

I'd suggest that you try to find a second hand resale outlet. In Pittsburgh we had a place called "construction junction" which sells all kind of parts from other people's renovations, including a ton of doors. You just might find some doors that can be converted into, say, sliding barn doors there. Good luck!

@yiyehtov
If the Japanese can raise their children with rice paper in the house, Americans can do it, too. American parents these days are too paranoid about "safety," and forget that children are not stupid and can learn not to mess with things.

@Sara
You might find Benita Larsson's explanation helpful. http://chezlarsson.com/myblog/2009/02/sliding-doors.html

This question is all over this site and to me there's not a great solution but looks like an opportunity for someone with ingenuity. This is a huge hole in the marketplace. What's out there is either somewhat cheap but not exciting or really expensive such as Raydoor or most recently I found a site via HDTV called 3form- http://www.3-form.com/solutions-ready_to_go_solutions-100_sliding_doors.php Really beautiful solution just horrendously expensive. Anyone know of anything like this for less?

3-form is some WONDERFUL stuff! Uh! I have built cabinets out of this gorgeous eco-resin for clients and they turned out just beautiful! We placed lights inside the cabinets, and the luminous glow is just stunning. For an inexpensive option, check out 3-form's remnants. Also, Lumicore is 3-forms competitor. They have a remnants page. Check out the collection of real botanicals sealed into the resin. You'll get so many ideas!

http://www.lumicor.com/index.php?option=com_content&task=view&id=195