You pay however much you are ready to pay.
Traditionally if you price a ware 100$, you'll lose all the money from those who can only afford 10$, and if you price it 10$, you lose all the extra money from those who would have paid 100$.
With Kickstarter, some people pay 10$, some 100$ and some 1000$, and they are all very happy about that.
This is achieved by: Giving nice perks for extra money; Buyers understanding that by paying less they only steal from themself.