This is why I refuse to remain a Prime subscriber. I do use the monthly plan once or twice a year (particularly the Christmas shopping season), when I know I can advantageously receive a massive amount of value out of it.
(If you have Prime and buy a new $60 video game, you get like $14 off, so buying Prime for a month if you're going to buy a game is pretty much free.)
Not being a Prime subscriber has afforded me often finding cheaper prices elsewhere. I buy from Target, Wal-Mart, Best Buy, Newegg, etc.
As for when I do shop Amazon: I wait until I have an order big enough for free shipping, which often means I am more hesitant to buy things rapidly and have more time to consider my purchases, it keeps my spending down overall.