Yeah I noticed it happening to me when I first promoted to ABBL. At the start of the season I was charging max prices and was able to sell out everything. After 2/3rds of the season when you have that arena prices change, my prices no longer cut it and was making a lot less despite me not changing prices at all and also finishing with a 11-11 record for my first season of ABBL.
So in conclusion, I reckon that the initial boost you get from promotion will wear out as the season goes on.
I think those prices are fair considering the initial promotion boost but the bleachers might be extremely hard to sell out if you do not win many games and as the season goes on