its an expensive habit, but I love it. If your asking will there be extra room in your budget, the answer is always no. Its a question of priority and what are you willing to do without? For me, I don't have a cell phone, I don't go out for lunch or dinner, I don't go to the bar, etc. Since you asked a legitimate question, here is an answer:
bike: $6200 (street and track), although I ride street anyways and already have a bike, so $0 in additional cost for track really. I bought an extra set of rims for slicks among a few other goodies, but none of this is needed for an entry level track rider. Most people spend $3000 - $6000 on a used track bike, if cost is your primary concern. Sky is the limit from there. You don't need a high $ bike or lots of horsepower to have fun on the track.
tires: this is usually your big cost. I run red group with race slicks and get 5-6 days on a set of pirelli superbike pro slicks ($350-$400/set). When you're new to track, you can likely just use a track oriented street tire, Q3, Pirelli DRC, S20, etc, at almost no additional cost (if your already using a sticker street tire). On the track you will use the edges, on the street you will use the centers. The tires will still go 4000-5000km on the street, you just get to use all of the tire, which is nice. You'd want to wear out the edges on the track first, then use them as street tires (which may mean 2 sets of rims to make life easy), squared of tires suck to ride on on the track, are more work, and have less room for error. So consider tire consider tire changing equipment if your riding track ($90 bead breaker, $20 spoons, $150 air compressor). The air compressor is generally a useful tool if your buying a house (flooring, roofing, cars, etc).
If you haven't done so already, you need to become skilled at fixing your own ride, mounting tires, etc. Having a shop do work on a track bike is prohibitively expensive.
gas: a tank for the day, so $20 (unless your doing mosport, then double it)
oil: change ever 3-4 trackdays ($50)
track fees: $100 for TMP on a thursday, $250+ for the big tracks (bogie, mosport)
trailer: $1000 5x7 (although I use it for many things, might be hard to store depending on your house. Get 5' wide if you can, not 4', so you can haul 2 bikes). Trailer hitch $250
parts/repairs - depends on how much you crash, engine case guards, spare levers, foot pegs, etc are a good idea. If you don't care about paint job, its not too bad. If you have a street ride you want to show off at the next Tim Hortons meet, could get pricey.
Remember, don't bring anything to the track your not willing to bring home in a box. Unlikely, and generally rare, but it does happen on occasion.
