I was in your shoes 6 or 7 years ago. I have been looking in every store I go into for interesting black and white post cards (about .50-.75 each) and hanging them up. Go to the craft store and get some frames for them (.50-$1 each) and make an interesting display on a large wall. There's no need to just hang them up straight accross, put them in clusters or groupings. You'd be amazed how many people have complimented me on my "art".
If black and white isn't your thing, you can use color but try to stick with some theme... all Van Goghs or all shades of red (something like that) to keep them complimenting each other.
I now have a large cluster of about 20 and the whole wall cost maybe $30 and I didn't buy them all at once, so you can set aside maybe $5 a week to so "art" shopping.
Another thing that works is to go to thrift stores and buy old paintings $1-5 each. Hang them as is or modify them like in this thread: http://www.craftster.org/forum/index.php?topic=29459.0