Spohn arms suck.

[mattbta]

Well, you've left out one type of racing that is one of the least expensive and safest ways to participate: autocross.

Aside from having an appropriate vehicle that's properly maintained, you only need a helmet, which most organizations have on hand as rentals. Past that, high-performance (or track-only) tires would be the next thing.

By "appropriate," I do not mean "modified for racing," I mean something that's not off-road-centric and/or liable to tip over. Competitors range from karts to Miatas to SSVs, in different capabilities and levels of modification. You're slotted into a class that suits your vehicle, so you won't see a kart against an SSV.

brakes and tires after a run aren't exactly inexpensive

 

[KidWgn]

brakes and tires after a run aren't exactly inexpensive

Far more inexpensive than an engine

 

[Scrappycrow]

brakes and tires after a run aren't exactly inexpensive

LOL, your brakes and tires aren't spent after "a run." They're not even spent after an event with ~10 runs. You can get a full season of ~70 runs on a set of R-compound tires and up to three seasons on 200TW-class tires. Brakes will last multiple seasons.