I wouldn't do elance or rent-a-coder for a few reasons:
Firstly, you might not be creating stuff that you will want to put on your resume/portfolio (my experience from that world is clients who want hacks and weird specs).
You will also find that going rates are pretty low because you are competing with off-shore labour (this is not a rant against off-shore, just an observation that this is how common markets work)
I have done freelance work through oDesk and the longer projects were quite valuable. Rates are low but not that low. According to oDesk's stats, the average rate for a web developer is about $16/hr.
Just put yourself up on elance / rent-a-coder, use that to build a portfolio.