I don't don't consider anything under $200.00 even if my art isn't worth that much. 100% payment up front, no refunds. No redraws. No picking from a series of thumbnails. That costs extra and is paid up front. I retain reproduction rights, and any ancillary rights. Depending on what you want, prices go up from there.
Oh, and in the "hard to work with" category, some subjects are off limits. Turnaround times are measured in weeks if I don't have other obligations, to months if I do have other obligations. I can tell you right now that I'd have to stop work on my comic to accommodate any commissions, and I have a loose deadline to meet on the comic, so even if you're jaw hasn't hit on the ground yet, you'll still need to wait several months until I can free up the time.
Their was a really good thread about commissions on the Press Oblivion forum that I took part in and details the reasons why I do things the way I do... Sadly the forum portion seems to have gone down today The main site is here...
http://www.pressoblivion.com/ ...and if the forum comes back up I'll look for that thread and post a link to it.