What are your favorite games? I'd check the credits of a game with graphics I like, see who the artist is and then search for their portfolio online. You'll have a better chance on landing an artist working with an indie studio, because usually artists at larger studios are over worked and have little time as a result.
I'd stay away from sites like Freelancer.com. Artists that bid on these sites underbid one another and are desperate for money. The site itself probably takes a chunk of that money. It's not healthy.
As long as the final result is good, I don't see a problem there.
Everybody needs to eat.
In order for an artist to become popular and charge more, he/she needs to work to build a nice portfolio.