What do you mean by buy the seat and retain it? Like it'll be reserved for you forever as long as you renew each season?
TAF requires that you donate to certain funds in order that you're able to purchase different levels of seats. This is how they're able to make the money they do. It's worse for football and baseball. I know that it was several thousands/seat to keep seats behind home plate.
If you did not choose to donate the extra, you likely wouldn't be able to get those seats again as you've be moved down a tier.