Here's my $0.04 from a guy that started in SCCA BECAUSE of the STU ruleset.
7-8 years ago, I bought a cheap 240SX for $1400 with a blown engine and put it together to run DEs... I built it the way
I wanted. Cheap, reliable, and fun on track..
Moderate engine mods: ebay Intake, early-model OEM cams, aluminum flywheel & crank pulley, Hotshot header, cheap aftermarket ECU, catback exhaust.. (All of these bought USED, btw)
moderate coilovers ($1k Japanese stuff built for the drift crowd),
$110 wheels from Discount tire, and a $400 set of used 5Zigen wheels for spares. Used Take-off R888s on both. full tread all-seasons on the stock wheels for rainy days.
A smallish (11.5") custom brake setup so I can run Wilwood Dynalites where pads are $56 a set and rotors are $60 each (and have lasted me over a year and I still have 1/2 the pad left!),
Sus Tech sway bars,
ebay rear upper control arms to adjust rear camber
That's the MINIMUM I expect to be done to a Nissan 240SX to make it decently quick on track. There are all kinds of JDM turbo engine swaps that can put you at 400+hp for a couple grand.. but I'm keeping the stock engine for cost and parts availability. You can go to any Autozone (or dealer) in the country and get a waterpump or a clutch for reasonable cost.
Fast forward 5 years and 100+ HPDEs and I want to go REAL racing- not just putting around the corners waiting for the point-by from the old fart in the vette in front of me that thinks we're drag racing.
I don't want to DE-mod my car. I want to put a roll cage in it and go play and see how I really stack up.
Now.. I go look at the SCCA ruleset and where can I compete? I have a car that won't fit (or be competitive) in Production or IT... I'm not going to go buy narrow 15" wheels (WTF mate?!) and cantilever slicks and stick the stock brakes back on... The factory anchors are junk and pads are >$400 for a full set. That's stupidsauce.
Sooo, SCCA is out.
I take a look at NASA's ruleset. Performance Touring is perfect! I can mod the car the way I want to, and tally up the points. blammo, there's my class. I'd run in PTD given my current setup.
Throw in a back injury and life outside of racing delays things a couple years. Now I've got the money for the cage in my budget, permission from the wife, and the time to do it.
I start looking at rulesets again and voila! SCCA has created this thing called Prepared/Super Touring. My car drops right in, and I can add cool stuff like wings and splitters when I'm ready to go faster, and it's not insanely expensive to run since I can run a stock engine and still be competitive locally (based on current lap times & race results).
Given my current lap times during HPDEs and lapping days, I'm competitive with the rest of the local guys running STU cause their car won't fit anywhere else. Go to a nationals weekend and I'll get my butt kicked- by about 2 seconds a lap given the nationally-prepped cars that have run here. But I don't really care about that right now- I want to get out there and race. IF I win, great! If not, well I was out there trying. And I did it in the car
I built the way
I wanted.
As for local participation, there are cars built specifically for STU and a bunch of IT and SM guys double-dipping, plus a Don Istook in his VW GTI coming over from T3. He's coming to STU because it's cheaper to run there than it is to run in Touring. so I'm not sure why people are complaining that STU is a money class...
You can run in it cheap or you can out-money the next guy, but you're still out there.
even in SSB/SSC, you can always be out-monied so why worry about it? go out there and race. If you lose, drive better next time.