Well I have a totally different experience with such sites. I have been a provider of wordpress, joomla, flash, etc solutions on such sites and find it is more than a bidding war. Some bids are so low you wonder how they are able to afford it. And its a wrong perception that overseas providers have the lowest bids. At times I have lost out to US providers who have bid at-least half of what I bid. Also the cost of living in some of the countries of the world is far higher than that in the US.
The main issue in our region with providers is that they are on a salaried job + they also do freelancing, and hence they can afford any price mainly because its extra income for them. But pure freelancers like me who only do freelancing or run websites are the sufferers as there are no fixed incomes to depend on.
Though sites like these have been a boon in professional life and it helps get business, I have seen that there is no continuity in work nor are there permanent relations. With 13 years of experience over 100 projects with 5 star rating (in last 4-5 years since I started doing freelancing on such sites) - Even if you do good work, meet deadlines, exceed expectations for the next project the process starts afresh. The repeat orders usually range between 10-30% on an average and each month you need to go looking for new work. Hence, freelancing is tough and there are lots of ups and downs as there is no guarantee of work once one is complete.
Hence, my suggestion would be to keep working up the ladder and sooner or later you will find a base and then you can decide whether that income is sufficient and take a call. Long work hours await you and you might need to work at odd times to meet project deadlines. The main income earners out of freelancing are the sites as they take money at each stage!