Jim had you thought of an early Gen 1 Cavalier Hatchback. I believe they'll run in FSP(check this) and they have tons of engine UD/BD available. The Gen one was available in 5 different bodystyles at one point. That'd be far less money than 8k too. Shocks might be your only Issue.
However the STS car I've been thinking about is a Geo Storm GSi not a Firefly/Swift. They can whip a Civic of the same generation and have less weight than say Aaron's car. So they're a good comprimise between power and weight. Lotus even used the chassis as the basis for the Elan S4 and used a turbocharged version of the Impulse RS motor. I'd own one right now actually but I can't afford to autox and get into roadracing at the same time. Another option on that same car line is the Impulse XS that has a 160 HP turbo engine for STS class.

They tilt the scales at about 2450ish pounds to the Storms 2350ish. Problem with these cars is the lack of development, you'll have to fabricate alot of stuff yourself or get it made.
How about a 75 Scirocco for SM, drop in a hot rodded 16v or G60. DYK that a Scirocco derives it's name from the hot desert winds of the northern Sahara that originate over Libya. How cool is that
Why not a shifter kart they are cheap, and you raced them when you were 4 so you have experience

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Another option would be a F500 car. They are uber reliable and can be roadraced and autoxed. An Invader QC-1 which is a top car can be had used for 10-5k sometimes with trailer and can be towed with a normal vehicle.
Just some more of my silly thoughts though

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