If it were me, I would take my hourly rate, say, $25/hr, and use that as a benchmark and then move that number up and down as I felt like it. It seems to me that it would be okay to bump it up a little bit, say $40-50/hr just to make it worth your time (if, for instance, you had decided to take a job in another field and would be using your spare time to take the consulting gig.)
But that's probably foolish, and why I would starve quickly if I were a consultant. So, readers, if you're a consultant, how should you charge for your services?
I've used a chemistry/chemistry-related consultant for regulatory affairs, once, where the
UPDATE: Let's just say that the comments are in agreement that my suggested rate is far too low. You should read them, and ignore me.