I guess I'm very cheap, but I'm not willing to spend more than 5 on a single game (unless there's a pricing error on a very recent release), and that would be only for AAA games. I may spend more on a bundle, but that's it.
I used to buy cheap indie games, but thanks to the multiple indie bundles now I refuse to buy a game unless it's been on a bundle that I didn't buy (i.e. I'll probably get 1000 Amps and Bonitacula if they're around 2 or 3 ).
So, what I really hope to buy is tons of DLC. The Chaous Unleashed pack from Space Marine, The Wrath of the Lamb, The Other Side of the Coin... If it's 75% off, I'll buy it.
With these rules, I've managed to spend less than 20 in every sale (well, in 2010's Winter Sale I bought the Valve Complete Pack). I also want to buy everything with a big discount, but I have self-control guys!