I don't like all their advice, but one thing that 37Signals does in this situation is just pay the person whatever rate they ask for. In the greater scheme of things, it's not a huge expense, and if you're to the point in the interview process where this actually makes sense, then you have a decent idea that this person is a candidate, and so you can invest a little in the process for everybody's benefit. It's a step beyond the whiteboarding "jump, monkey!" coding interview.