Firstly, nice shot.
Secondly, before thinking about pricing, think about printing, as in where and how to get it done. You didn't mention yourself if you had a printer (and how good it is), or were you planning to go to a lab?
If you've never printed (big) before, the best thing to learn is that screens and papers look very different, you might go through a few paper-sample-packs before you find something that matchess well with what you're printing, especially as your buyers saw the shot on their screens. If you've got a printer at home, try out a few papers and profiles and whatnot to see what would look best, or ask your local lab if they can give you some smaller prints for a sample.
(I'm lucky, in that I've got an Epson R3000 which goes up to 13", if I want wider than that my local lab has the larger epson 4800 or something which uses the exact same inkset, so that it'll look the same just larger).
So if you want that big, unless you've got a 20" printer already, you'll be going to a lab to get it done. Start by asking how much it's going to cost you to get it printed. For example, my local lab charges $120 for a 60x75cm (24x30") print onto "fine art" (etching/museum rag/metallic pearl/etc), or $60 for a regular "photo print from digital". Then maybe double or triple that to cover all your work, gear, test shots, etc. (or if you're nice and doing it for friends, just give it to them at cost plus a few bucks)