Depending on the game, you can often find very reasonable tickets outside the arena. For example, I saw plenty of Texas tickets for $20 or less last weekend.
As for the upper levels (200 and 300's), the closer, the better (of course). From the side or corners, you are in good shape if you're close. TB is a big place, so be wary of the nosebleeds.
As for moving closer into empty seats: I wouldn't count on it. The ushers are pretty tight about checking stubs.
Hope this helps.