When playing with the expansion can a player bid on the banker even if he doesn't have the cash for his bid? (this is generally forbidden in the expansion but when taking the banker your bid is subtracted from the banker's money!)
Yes, you can (the cash to pay the auction is directly taken away from the banker): the banker is the way to get cash without having any (because using the expansion you can't sacrifice points for cash like in the normal game).
I didn't even know there was an expansion for this game. Is there a link to a BGG entry? I couldn't find one on the PoF page.
It is not a separate expansion but included in the new release of the game by Quined Games/Ystari...