Did somebody put you up to this - just to get me going on this idea? [I'll add I've been in South East Asia and for the past 5 months been preping our sailboat for an Indian Ocean Passage - not tending my cars. This break is much appreciated]
I note you never said you were interested in standing on the podium, but want some speed, more safety, and contain costs? Why not keep it as simple as possible - start with an available purpose built race chassis, and modify.
1. Get a used Gen1 or Gen2 SRF. It is not a tin-top Mazda. It has center seating formula-style, unlike many of the 2 seat Sports Racers.
2. Purpose built, dated, but well-known technology.
3. Available; I see them listed as low as $5-6K for Gen1 Renaults, $12K for good Gen2s and $20+K for excellent Gen2s. These are going cheap as guys are leaving rather than convert and retire.
4. Pull the engine/tranny - replace with a --------- (you fill in the blank) under 2.5L -- No turbo/supercharger (I'd Suggest to use auto engines - not bikes) I like and am leaning to a TRD/2ZZ 190HP-ish or Honda equivalent. With these engines you could have the speed - just choose not to use it - keep to FF speed.
5. Nearly anything goes aero, wings, etc, Carbon Fiber body - different body entirely - your pick. You pick who builds your engine, transmission, sells you brake pads, etc. Autozone/eBay - you choose. You choose whose and which tires you want to run.
6. Reg as a SPU - yes it is a regional only class, but if there was effort and some constraints, it could be another (oh-no- not another class!) I should look at the national class count for P2 & P1, but SRF is about 900 cars.
As a buy now, race some, build project, you could distribute the costs over several years.
If somebody wanted to write a classification guide, they could set the minimum weight at an unrealistic 1200#. The SRF body and chassis is heavy - but solidly built. There could use a NASA-like formula for points/discrimination between builds/cars. Track days and AX/hill-climbs all available, and if clever depending on state - could be street legal - that's a scary thought. With a change of body work, it could re-materialize as a Formula-S, but again, perhaps with a weight a penalty.
In SEDiv SPU often is classed in the same run group as the SRFs. The car I've outlined could run at the head of the "Spec-Class."
Thanks for getting me off the "boat" for a few minutes.
Cheers - Jim