If you can't already afford the Vette then you would be better off w/the Stang. Mods are cheap, and generally won't break the bank. The Vette mods are seriously out of my budget.
Plus IMHO, when both engine blocks are pushed to there threshold, both engine blocks would put out the same numbers.
If I can't afford to replace a car, stock of course, then I wouldn't even think about purchasing the car.
Both are excellent vehicles, I've seen a lot of Vettes around here, in fact I've seen more Vettes then Camaros. Go figure.