As a consultant myself, I spend about 60-70% of my time on over-head, finding work, negotiating work, dealing with the paperwork involved, etc. The rest of the time is spent doing the actual work, this is something a lot of people don't realize when they see those sky-high consulting rates, I charge $185/h(varies depending on type of work) but I'm actually working 3 hours for every 1 billable hour I end up with.
So take that into account when thinking about your rates, that's a mistake a lot of beginners make.
These days I get a lot of my work through reputation, but I've been using Elance for awhile, and have personally never had much issue demanding my full rate. Yes you're competing with low-cost offshore talent, but there's a market for local or in-country talent etc, and depending on your work, it's not hard to convince people. For instance, my rate seems really high, except I have a performance record of doing things 3-5x faster than a lot of these off-shore guys who are low-mid 20s guys with just a few years of experience.
That is to say, I'm an actual professional, where 90%+ of elance/odesk/etc are just pretenders who try to entice with low rates.
It's very dependent on the type of work as well, speaking more specific to my field, most of my work is doing system architecture as opposed to just "coding", I get hired to design large systems and then they hire those other guys to implement my designs.
Also, keep in mind, about 1/4-1/5 of all your clients ARE going to try and stiff you. There's no way around this, build it into your rate, cause it's just reality. The cheaper the contract is, the more likely people are going to try and stiff you. Lots of companies or shady guys make payments based on how likely you are to sue them. Suing people over a sub $2000 bill often isn't worth your time, but sometimes you have to just send a message and make the sacrifice. It's annoying, and just starting out you'll probably deal with it more often than when you're established.