Have to buy each month? no other game works like that on here... buy it once and you get every update. Cant recommend putting any money into this project if thats the case. Are there going to be 8 dollars worth of updates every time it comes out?
this must be your first time seeing it however there are quite a few that use this method and most of them are much more expensive than this so i would say for whats in the game currently 8 per update to help support the development is fair, they need to pay there bills too