I've seen people who base their prices on time, as they set themselves an hourly rate. Well, this took about 3 months, of very sporadic work. No idea how many hours, and a lot of them were just unproductive deliberation. Can't really charge for being hesitant.
I'm in the UK, so will have to work on £, but £200 -£250 would probably be about right.
Do any of you use etsy? How good is it for selling paintings?