We just finished renovating the bathroom in a rental apartment. The before image doesn't quite capture how uninviting it was. The shower stall (and I use that term loosely) was made of flimsy shower panels held together by wishes and a couple of screws, just big enough to get clean while knocking your elbows and knees on the walls. The plumbing, coming up through the floor from the basement, was dangling on the far side of the shower wall. The bathroom was dark because the only window had been boarded up with plywood and covered with wire shelving. The overhead light/fan combo cast a dim yellow glow over the room, and the fan vented to the crawlspace above...and no further.
We did a gut renovation, tearing everything out to the studs and subfloor. We had professional help to relocate the plumbing, but everything else was done by us - installing new foam insulation on the exterior walls, new cement board and water-resistant drywall, new subfloor, new vinyl floor, new shower, new vanity, new light and fan (properly vented), new window and trim.
Our original budget was $2000, and our final cost was close to $3000. This includes all materials, fixtures, paint, trim, and labor. Almost everything came from Home Depot or Lowe's. The biggest expense was the professional plumbing work ($1600), and the next biggest was the new corner shower (about $400).
It looks pretty stark now, but we hope it will be a bright and inviting space for the next renter to personalize and enjoy.