That is the worst question to ask someone when you are trying to negotiatie a sale. It's like "Dude, bid against yourself, and tell me what is the least amount of money you will possibbly accept." Who wants to deal with that?
A better approach is to ask, "What do you think a fair price is?" And then take it from there. That way you don't come across as...cheap and rude.
"Nancy Ninja Nabs Nefarious Nymph. Pays Price Per Pissed Pants!" -Flick
"Up, up, my people, let smoke and flame be our sign!"
-The White Rose Society