The fact that someone wants to buy it proves you are wrong. $10K is nothing for a company. It cost them $10K to decide to offer you that much. Unless you really would not sell at any price, ask for a truly big price ($100K+ ?) and see what they say. The worst that happens is they say no and you are back to where you are now. If they didn't think they could grow your project to be worth millions, they wouldn't bother with you at all.