Two particular cars come to mind.
Mini Cooper S - not really a muscle car killer but for $20K there is very little that will touch it. 175HP (conservative) from the factory. Easily possible to get 200 - 230 HP without too much money. Difficult to get the power to the ground without a LSD ($1000 + 12 hrs install).
Cooper S (stock) will see off a Subie WRX, Audi A4 or S4, BMW M3's in an autocross enviroment. Will blow off A4's S4's, WRX's, 3 series (not newer M3's) and bikes up to 750 on the local race track. Twisty Canyon roads in 2nd and 3rd gear are it's forte. But higher speed tracks require too much HP for the Mini.
Hence (my wife's new chariot)
The Subaru WRX STi (Subaru Technica Inst. - kinda like M Beemers or AMG Merc's). 3500 vehicles a year into the US, 2.5 liter turbo'd horizontal 4 putting out 300 HP (255HP at wheels). AWD with driver controlled center diff and LSD's in both diff's. Lightweight glass, no radio, not even floor mats. Intercooler with water spray. 17" BBS wheels and Brembo brakes - $31K.
Definitely not your 230HP standard WRX.
This car will easily blow off (yup, easily) Vette's Stangs and Camaro's. It will surprise a Z06 Vette to 100mph. 13.1 secs - 1/4 mile bone stock. Races in A Stock in SCCA, usually the domain of the Vette's.
Without a doubt the most violently fast car (road car from the dealer) I have driven. Similar power delivery to the Porsche 911 turbo's, 930's here in the US, without the oversteer handling. A Vette and Stang may hang in a straight line but come the curves this car leaves them eating dust. AWD certainly helps, a smart center diff makes a big difference, but it can also be manually controlled, locked to 50/50 front/rear.
Not an easy car to drive at all though. The two LSD's can become a b*tch when they do grip, pulling the car in all directions, especially when you are on the boost. Requires a rally style of driving more the typical smooth lines. Versions of this car won Pikes Peak and the World Rally Driver's Championship in 2003.
I have a friend in Detroit who is producing 430HP, that's over 350HP at the wheels - all 4 of them, with very few mod's. No cat's, downpipe, intake, boost control, fuel management. bottom end is built strong, so I could see over 500HP - streetable, would be possible with a bigger snail.
Current wait times in CO, Mini Cooper S more than a year, WRX STi about 8 months.