Racing is expensive.
To minimize this as much as possible consider running in a "production" class. Lots of people are having a barrel of fun racing Ninja250s all over the country. These little bikes are relatively inexpensive to purchase and maintain and the allowable modifications are few. Tires are a little less costly and they don't go through them quite as quickly.
Grids (at least on the West Coast) are reasonably full in these small-bore production classes providing lots of opportunities to "race" no matter how deep in the pack you're running.
Be realistic about your goals.
Remember that you're racing for a $5 plastic trophy...
Develop a budget then double it. (That should get you close and if you're lucky you may have a little left over)
Consider the points above about your health insurance. Study your coverage carefully.
Most organizations won't let you on track with out insurance so make sure yours is actually going to cover you.
Get Helicopter insurance!!!
Out here it's ~$25/ year and that covers 100% of an "air-ambulance" ride.
Many personal medical insurances don't cover this and if you're unconscious at the track, chances are you're taking a ride...
You don't necessarily need to be running an "A group" pace to go racing, but you do need to be really comfortable with riding close and aggressive.
"The ninja got a bit fruity on me down the corkscrew." -Tom Sykes, Laguna 2014
10' Husaberg FE390, 05' ZX636R TrackBike, 00' XR680RR SM
04' CRF230 Flat Tracker, 02' CRF150F, 66' CB160