You don't want to go to low for risk of undercutting yourself and you don't want to go to high for risk of them rejecting and walking away. If they are very keen on your work they will negotiate with you. Remember that they have costs such as buying the canvases, printing and postage which will probably be quite high. I would probably go in at 25-35% of the sale price (not profits which would be significantly less). If they plan on selling in large quantities you should make a nice amount of money out of this. I also wouldnt be too adiment on the % you want since they could walk away and leave you with nothing. For something that will require not much effort since you have already taken the picture I would be prepared to negotiate freely since some money is better than no money. But don't let them push you around
