The breakdown for a Volvo 244DL that we built for a full 24 hour race for "that other series" is more or less as follows (That other series has almost the same rules for car prep as the Lemons event you guys are prepping for):
$100 1989 Volvo 244 DL with 300k miles, not road worthy, good engine and tranny
$60 seat and seat cover new including shipping
$10 grade 8 hardware for mounting seat (buy grade 8 by the pound at Tractor Supply)
$200 brake work, new fronts plus extra pads, spare used calipers and master cylinder
$100 spare parts for race, used fuel injection computer, radiator, tie rod ends
$100 parts for suspension repairs and drive train repairs to make it roadworthy + water pump
$600 for two sets of new 14" tires including shipping
$40 for a spare set of 14" wheels
$80 5pt harness
$20 roll cage padding
$300 ERW cage kit shipped, self installed, racepartsusa.com has these kits.
$30 extra ERW for finishing cage
$45 FIA kill switch with alternator protection
$20 driving lights kit from Wal Mart
$100 estimate for little extra crap like, spray paint, duct tape, bolts, rivets, liquid nails etc...
$20 windown net
$60 consumable fluids, motor oil, diff oil, clutch oil
$100 estimated towing fuel, the race is only a 3 hour tow one way
$400 estimated racing fuel, around 1200 to 1400 miles including practice at around 10 mpg
TOTAL $3085
A new team might need to add $50 to rent a transponder and $50 per driver for racing licenses. But I'm sure there are guys who could do the same thing I did for less money. Although probably not much less. In some cases it will cost more. Anyhow these are some of the main expenses.