i want a bulletproof transmission........

I want to get another 904 for my car that is more than the stock rebuild. I want a low gear set, with good bands, and a reverse manual vb with low band apply. In addition a bolt in sprag for good measure. How much would a 904 like this cost me?

I will be going behind a 340 with a 4500 rpm converter, car has 4.56 gears and will be on a set of et streets. I just want to make sure that I dont break anything.