It's worth not being put off by the 20 dollar offers, a lot of people don't take them seriously and only look at the more realistic offers and if they do go for one of the ridiculously low ones, they almost certainly aren't worth working with.

The word of mouth jobs in my experience generally pay better and tend to be more interesting but I've had good experiences with freelancer.co.uk in particular when I've wanted bits and pieces while waiting for bigger pieces to start etc.