We've used Cost Plus World Market many times as a source for simple, inexpensive white curtain panels. They're sold in pairs for around $25, and ours have held up well in our own home. Right now there's a sale on window coverings, so prices are further reduced. The standard size is 84 inches long, but if you have extra-long windows, you can spend a little more and pick up two 216-inch white swags (sold in individual panels). Draped over a curtain rod, they measure 108 inches long, which is usually enough for tall floor-to-ceiling drapes. Links below.