tranny swap

hello, I have a 2001 chevy 2500hd with the 8.1L and Allison tranny. I have put everything on this truck from the six inch lift to tow hitch cover, all in all about $10,000. i love this truck except one thing, the tranny. I would love to turn this truck into a manual tranny. anyne ever try this? if so how much did it cost and is it worth it? thanks