Actually in the revised rules it elaborates and says:
Amendment to Rule 4.2.1 part "# Wheels, tires, and brake components" changed to "# Tires, brake pads and Brake discs/drums" Reason= to stop people spending $4000 on a Brembo Big brake kit or $1500 on some nice rims.
E.g it limits to consumable items
I wouldn't consider trademe value to be fair and equitable for a lot of things, way too variable
another question I've just thought of, what about costs of fabrication? e.g cost of steel/alloy/etc
Service related items for the engine? oil/filters/etc
Getting together a genuine $700 car then welding in $1500 roll cage and $500-1000 worth of seat and harness would get a bit depressing, especially considering the disposable nature of the cars
If you're building it for a 24 hour race, that's one thing.. but 2 hours isn't all that long.