Java fern, as you mentioned, is an easy one. Java moss as well. Water sprite, Crypts, dwarf hairgrass... these are all relatively low-light/low-tech plants. I'm sure there are others, but these are the ones I am most familiar with and actually have in my tanks (all low-light tanks, no ferts, no CO2, etc).
I recommend a pool filter sand substrate. Not sure what you're planning at this point, but so far that is my favorite substrate. I'm sure the Eco-Complete stuff is great too (pricey though) and for a low-tech setup, probably it's not all that pertinent to use that type of a substrate. But it wouldn't hurt.
Post pics when you're actually starting!
Oh - and plenty of people here are willing and able to sell plants cheap and ship them to you. I was cleaning out my tanks recently and was shipping out 6" x 9" packets of java moss and water sprite for $3.50/each - and I've seen plenty of other people doing similar things. Watch the classifieds thread and I'm sure you'll see plenty of good plants for sale at a good price (often cheaper than buying at the store in the first place).