The Contrarian method:
Gas: $60 (that's from SE Michigan, in a Dodge Neon)
Campground: $25/night, three nights ~= $80 w/tax
Badge: $75 (I registered late)
Events: $11 (I do fill up on free events, though, so I have someplace to go if I'm bored)
Food: less than $20/day -- I ate breakfast at the campground, stuck to cheap fast food for the rest of the day -- the real killer is those $2.50 Cokes in the Convention Center vending machines
Parking is hell: $55 over 4 days, but I was lazy in looking for parking garages. I probably could have kept that under $40 if I'd been willing to drive around a little more.
Shopping: I kinda lost track. (I have to stop doing that.)
Looking at my bank statement (I paid everything by cash or debit card), it looks like I blew about $500 on this trip. About half of that was "unavoidables" -- badge, gas, camping, and food. The rest was just me being frivolous.