I think this would be cool, but I think it would also be kinda overpowered. If someone is saving their souls to get a kiltons set, for example, and they get 7/10k souls needed and a very high price was offered, then the players with a lot of money would get any and all great things out of kilton with little to no effort. Yeah, heads are sold, but they take a while to accumulate. I think being able to buy souls in a really big number would be overpowered. Maybe it would balance, I just don't think so :)