[txcwpalpha]

>The percentage that is overhead will vary, but only by so much. Otherwise, someone will come along and find a way to undercut your prices and take your business. It's reasonable to assume that if one hourly cost is double another, the developer's pay is higher.

That's really only true if you assume that all of these dev agencies are equal. In reality, a lot of them have different specialties (both tech wise or industry wise), better (or worse) reputations, or certain partnerships. All of these things can greatly change the amount that the dev agency can charge.

I've personally seen plenty of agencies charging $100/hr while another agency with a different "specialization" (but otherwise similarly skilled and paid devs) charge $250/hr. The bill rate hardly ever corresponds with salary, IME.