I'm thinking about putting an Infinity Perfect 12 in my car, and
powering it with the Alpine MRV-T420 amp.

While trying to do some research on the amp, I found that there are HUGE
price differences from one dealer to the next.  For example,
etronics.com has the lowest price I could find ($165):

http://www.etronics.com/product.asp?icatid=303&stk_code=alpmrvt420&svbname=293

So I did a little research on etronics, and customer comments seemed
pretty polar (oustanding or horrible).

The "well-known" places (Crutchfield, American, Circuit City) are
selling this amp in the $350 to $400 range.

How can their be such a huge discrepancy from one vendor to the next?
Is this typical of car audio products?

While I'm at it, anyone have experience with this amp?

Thanks,
Matt