Taj Mahal, anyone?
Once this happens, and you choose to buy, can you buy as many as you like?
That's not the way we buy/sell goods.
Or is this process PER GOOD?
Yep, that's the way we buy/sell goods.
If I had a monopoly on certain goods and my opponent was going to buy 2, I would certainly want to charge him more if it might give him 2 full warehouses for example. But if he was only buying one, I might ask for less.
Yep, that's the reason why we play the process PER GOOD.
It's not clear in the rules how to handle it.