I find mine on oDesk. Rates vary widely; good talent is always worth it. I'm paying between $12 and $38/hr.

I post a small gig, with well defined deliverable. Then I have like 100+ applicants. I use a tool I created to filter this down to four or five.

I'll do a quick interview, ask for code or something and then hire two of them for the same gig.

I evaluate their work over this short period (10-20h).

I pick the "winner"

The cost of this hiring via experimental gig is very low and I've had good results thus far.