Somebody could offer it sans HTML/CSS, charge $150 and still stay busy IMO. My basic mate's rates fee for that sort of job is $1000-1500 for a PSD.

That said, $15-20 is comfortably in that "If it doesn't work out, who cares" bracket. The problem will be that for many people, time is far more crucial than the cost. If I need a turnaround of 3-4 days, and the queue is 7+ days, it won't matter if it's $15 or 15 cents.