Would also like some advice on contracting app art. A game I started as a personal learning project, is growing and some good consistent art would be of tremendous value to it.
You may want to dig through the pixeljoint and way of the pixel if you want that particular style. If you are looking for artists more generally, the tigsource forums have both places for posting portfolios and job offers. I think that polycount forums may have places as well, but I am not as familiar with that one.
The point is that a ton of game artists hang out online, and you can get to them through there. I am pretty sure that some of the superstars do contract work as well. Paul veer did super crate box's animation, and as of 6 months ago was taking on freelance.
However, the artist we hired was an ex-coworker of a friend of a guy that we met at a hack day, so just getting out there and meeting other game developers can help as well.
Regarding costs, it is generally cheaper to hire an artist than a programmer, but not by much. Maybe 2/3 - 3/4 of the cost of a good programmer. You certainly are not going to get solid work for free.
