You are probably using money from your game. From what I heard, money is not displayed the same between the Manage my team page (which I don't use) and the Economy page. It's probable that on one of those you have the money to bid.
It's impossible to bid money you don't have.
Right. Although it's likely too late to benefit the original poster, while you can not see the amount of revenue from the home game, sometime in the 15 minutes before the game the "Last home game: XXXX fans" updates on the manage my team page. That can at least give a rough idea of how much money you'll have in addition, though the usefulness of that is limited.