During the September special, I paid $6.99 for 5 credits, but got 10 extra credits for buying credits in my first 30 days or whatever, plus 25 bonus credits... so I basically got 8 seasons for $7, less than $1 a season. 8 seasons is almost a year playing 2 teams. I think that's a great deal.
Plus, if you have someone use your referral link, you can talk them into buying credits and get 10 free credits, or two free seasons. You bring one person on board, and they buy just 5 credits, you get 2 free seasons, plus they get 2 free seasons.
I only bought 1 season to check the game and see how it goes, plus the great September deal where you get 25 bonus credits. If he runs that again, you should jump on it. 6 seasons for $7 is a pretty great deal.
And, finally, if you like the game, you should really just spend the $40 like Zoot said. You really can't beat the deal. But $40 when they have the 25 bonus credit special, and it's an even better deal. You really can't beat that kind of deal.