I don't know how to feel about the current trend where Early Access and Alpha/Beta are sold at a higher price than retail release. On one hand, you had Bohemia Interactive going into EA with ArmA 3 where the earlier you bought into it, the more you saved until it hit the price of $60 at retail release which felt nice as an early adopter. On the other hand, you have...well, almost every single Kickstarted game that sold early access for more money.
Anyways, I think you should add a few more tiers for multiple copies of the final release of the game. Since it's $20 for a copy(as per the unlimited KS tier), then maybe $36 for 2 copies, $52 for 3 copies, $68 for 4 copies, $84 for 5 copies, $100 for 6 copies, and so on.