Designers often say a great way to display affordable art in your living space is to frame prints or cards. I've taken this to heart and did just that last month after returning home from California with a few handsigned cards by artist Susan Hall. I recycled unused Pottery Barn wood gallery frames by replacing old, tired mats with new crisp white ones and voila--an entirely new look for a reasonably low price.
$3 for art / card
$15 for Pottery Barn frame (bought the floor sample at half off)
$24 new gallery mat (off-set just a bit)
$9 assembly, wire, paper, etc.
So until you decide to hang a Picasso above that fireplace, consider this tip to tide you over :)
I also found some beautiful (at least I think so) art at a local gallery/framing establishment. They have many works of original art for under $100 (some even under $50!) by artist Jodi Steen. If this is a style you enjoy, it's a great deal. In Michigan, you can find her here. But you will find significantly better prices here in Salt Lake. I like her muted pieces best.
Here is a picture of the little piece I bought a few weeks ago. I absolutely love it.