I look at the expenses from the aspect of not only tires, but also insurance (bike + health), vehicle transportation (for all my track days I have been able to bum rides from friends who were also going who had a truck/trailer), a 1 piece suit (I currently have a 2 piece), maintenance on the bike (brakes, suspension tuning, gas, oil changes, water wetter, tune-ups, etc). It all adds up and I am in no position to even think about getting more involved than just track days here and there... Gawd... as much as I would love to.
as far as expenses go, I don't have my racebike insured - when doing trackdays, I kept insurance on it, which worked in my advantage because I wadded it up last year and got a shitload from my insurance (stated value full coverage FTW!) without getting it totalled...but insurance won't cover your bike if it's damaged at a sanctioned race event, so there's no real reason to keep insurance on a racebike. For a trailer, you can pick up a 1-bike trailer and a small receiver hitch that will go on a Honda or other small car for around $450 for the trailer and hitch, and that's plenty for raceday/trackday transportation - shit, you could pull a small trailer and a bike with a CRX no problem. When shopping for a suit, don't worry too much about buying a big badass expensive suit, before I bought my baller-ass A*Stars I had a Frank Thomas that I picked up for $75 off of Craigslist, and I went down in it at LEAST 4 times last year, and for being a cheapass suit that supposedly wasn't worth a damn, it sure did work pretty damn well for me. If you're on a budget, Frank Thomas suits are a definite 'win' - don't listen to the people who say that they're junk because they're cheap.
As far as maintenance on the bike goes, I wouldn't worry about water wetter. The first few races of the year here in Texas are usually cold as hell in the evenings/mornings, and usually gets below freezing at night, so my bike spends the night of the first few racedays with no coolant, and I just refill it with distilled water before practice sessions in the morning. Brake pads are about $50 for a both fronts, and usually get replaced every 4 race days. Don't worry about the rears, you shouldn't be using your rear brake on the track anyways. For suspension, you'd be looking at around $40 to have a reputable shop set up your stock suspension, and that should be fine for you throughout the year unless you gain and/or lose a LOT of weight for some reason - don't worry too much about spending lots of money on baller suspension until you reach the limits of your stock stuff.
All that's stuff to keep in mind when/if you decide to jump from trackdays to racing...just my .02
Also, ditch the chrome windscreen...looks pimp on the street, but you'll want to be able to see where you're going when you're at full tuck on the track ^_^