With rare exceptions, nasty boys probably sell from 1/2 to 2/3 the price of a stock restored model. Some of the professionally done ones are best compared to the hot rod/street rod market where they can bring big money at an auction if they catch the eye of the right buyer. On the low end of the scale, you can probably pick one up for about $5k if it was a really shoddy job done back in the day. They appeal to a rather small market and face stiff competition from kit Cobras for someone who wants a V8 in a small British car. I think the days of big fender flares and holes in the hood are, for the most part, past as the newer builds seem to trend toward keeping the exterior looking stock while modifying the driveline and suspension. One of the problems with increasing horsepower is getting enough tire on the rear to harness it. The old way was to flare the rear fenders to fit wider wheels, but some of the new cars like the one posted here, widen the whole fender making a smoother appearance.