"because of the design of the car, the wind blasted you at slow speeds when driving. "
That's ridiculous. How can there be wind issues at slow
speeds unless you're in a tornado? I have no interior wind issues whatsoever, even at high speeds, as the Challenger windshield is inherently tall; as compared to the Mustang and others - and I'm 6'4"!
There will be some quality concerns with any radical custom; heck, the new Camaro convertible is outsourced to a German company and there have already been some quality complaints. As with any convertible, as long as the car is structurally solid, it is worth the investment. The small stuff can be easily worked out.
If your serious about buying a good used one:
Hemmings Motor News: Dodge Challenger for sale
I will be buying a leftover SRT 392 for my next conversion, but this one is aweseome; especially for the condition, price and very low mileage.