Are you looking to stay in a stock class, a SP/ST class (coilovers, wheels, tires, race seats, wheel, sways, I/H/E, etc) OR you could do a full out E mod build (would not be street legal)
If you want to do TT or just track day events, your budget will increase by a good amount. For trackdays, my budget ranges from 100 bucks, to $1000 depending on the organization.
Your going to have to remember these cost...
-brakes
-tires
-fuel
-fluids
-food
-entry fee
-gas to get to the track
-hotel if out of town
-tools
-racing gear
and the list goes on. Pick a organization and a class, and then build a budget for the year that includes everything including the car build. You might have to do an event or two to figure out how much you plan on spending a year.