I don't know where did you get the $90 number. the price for the early access version will be around $20, the full version - $40.
I understand that not everyone is able/willing to pay for versions separately. but you don't have to! if you don't like the idea of paying for each update - JUST WAIT for the EA or full release and pay once.
at this moment of development, we can not put the game on lifetime ownership, but we will on the release of v0.9