Tranmission help!

I have recently picked up a 91 s-10 with a 355 in it putting out about 400hp, it also has a 150 shot of nitrus added to that.

At the moment it has a turbo 350 and 373 gears in it. Which very well means it cant really go over 60 cruiseing. Seeing how i'm going to be driving this thing around for the time being i'm putting the old 273 gears in order to get some kind of efficiency on the highway but i'm wanting to put an overdrive tranmission in it and the best looking one i've seen so far is the 700r4.

I've shopped around for priceing and couldn't do this swap myself by any means. Does anyone have an estimate on how much the transmission plus the labor all together is going to cost me? Also can i trade in or sell the turbo 350? It has a shift kit and all. If i can what could i get for it?

Also there is a ratcheting slapshifter on the transmission. Can the same one be used on the 700r4?

Thanks alot for your help.