The problem is IMO that "non-boring cars" and "reasonable prices" are mutually exclusive. Apart from the Abarth 500, all of the listed vehicles are quite expensive, thus making rental of these vehicles more expensive.

Just for the sake of comparing it to US performance vehicles: A Golf R is somewhere between 43,000$ and 52,000$ before taxes in Germany and thus a lot more expensive than a V8 Mustang. The other cars are even more expensive, which explains that the rate are so pricey. The rental agency is going to eat up a lot of devaluation of these cars.

Moreover, these cars IMO don't fall into the fun car category (with the exception of the Golf R and the F-Type). The cars, you picked, are massive and won't be as much fun on the narrower roads. A small hatchback with go-kart feeling is the way to go .

If you want to go exotic, it's probably best to look for smaller agencies that specialise in this kind of rentals. I know that major cities have several of these companies.