It's an old thread and an old topic in general, but it's fun to speculate so here goes:
Realistically, there isn't any reason you can't get away with 10-12 psi on a good stock shortblock and a blower. If you're stone stock at around 190 rwhp, and you put on a blower at 12psi, you will not see more than 345 rwhp. That is the ideal increase in power at 100% efficiency 190 rwhp * (12/14.7). If you don't understand that formula research atmospheric pressure and the effects on boost on power - it's a rule of thumb, but is pretty accurate.
Of course, blowers are no where near 100% efficient, and also your average centrifugal blower will not make it's peak boost of 12psi at the same RPM as your engine's power peak. In fact, your centrifugal blower will not make much power at low rpm because the boost rises linearly with rpm. I think you'll find, in that case, that the H/C/I engine will make better low end and the blower might* come out on top on the high end.
My money in this race would be on the well thought out H/C/I combo in a heads up race. I'd figure the cost is a wash. Ease of installation definitely favors the blower.
Here's something that would bother me, though. The guy with the 11 second na 302 car is going to impress a hell of a lot of people (ask me how I know
), whereas the guy with the blower is going to get mixed reactions. A lot of people will expect a supercharged mustang to be a monster. A lot of people will have much higher expectations of a supercharged car. My turbo car, for example, only made 420 rwhp, but my far more impressive to people na 302 made a fantastic 320 rwhp. Which was more fun?... Pretty close decision. I sure always liked being the under dog, and outran at least 3 different supercharged 5.0s with that car... I had people like them asking me to show my non-existant nitrous bottle. 420 rwhp just isn't enough power to meet the expectations of people who think turbochargers are the end-all of performance.
Realistically, I think that if you put in the work, you can H/C/I it for the same price you can blow it. It comes down to what you want more: ease of installation and the impression having a "supercharged" car will bring, or sleeper, more reliable, and probably slightly quicker.
Good luck however you may choose. I think you'll be happy either way.
Chris