what tranny should i use? help

So I have 92' 2200 ext cab that I'm going to use to haul a street bike 90% of the time. It needs a tranny but I don't really know what fits. Need some help deciding what tranny to go with, considering things like money, gearing, n mpg.. mpg n money being the most important. Lol .. i heard from a friend an rx7 tranny will work but what gen rx7 tranny n how will it change the gearing/mpgs? I appreciate any info. Thanks guys