[samlev]

The short answer is "You get what you pay for". There are plenty of 'cheap' contractors who get as many jobs as possible, churning out bad code that kind of does the job. Most of these will be "copy and paste code" style contractors who only write a little bit of relevant code to make it look "right".

I would, generally, avoid any short-term developer who's charging under $50/hour.

The other thing to note about elance, vworker, etc. is that there are a number of companies in very low-cost places (such as India, Pakistan, etc.) who will then re-distribute the work to their own employees. They tend to produce very low quality work, and there have been some horror stories about these types of developers using the job to insert nastiness into your site for their own ends (why hack a site to insert your malware when someone will give you access and pay you for it?)

YMMV. Treat them like any other person you want to employ and check them out before giving them much access or responsibility.