I'm not cheap but I'm only willing to pay what I think a game is worth to me. To this end, I use a tiered system to determine which purchases to make:
-Tier 1: the full-price purchases I know I'll really, really enjoy. Dead Space, Dark Souls, Fallout, Red Dead Redemption, etc. I'll gladly drop $60 on them.
--Tier 2: reduced/sale/used purchases, games for which I'm only willing to drop $10-$40. The vast majority of my purchases are on this tier. Mass Effect, Grand Theft Auto, the recent Silent Hills, etc.
---Tier 3: free. The bottom of the barrel, the garbage, the products from developers whose timely demise would leave me quivering with elation. Bioshock, Skyrim, Bulletstorm, Call of Duty, Halo.
They'd have to pay me to play anything beyond that.
I've never bought a special edition yet and the only bonus item I regret missing out on was the Vault Boy bobblehead from FO3, but even then not enough to track one down on eBay. I already collect action figures and have a lot of other non-gaming related hobbies so I don't have the spare room for that junk, nor is it usually worth the extra money.