well im the kind of person that will spend a few extra on parts to get top notch customer service... i get everything from jeff at FAST casue i know if theres any problems he will take care of it...
before you go dropping a cub in there... what kind of riding you do? if your a trail rider dont bother... you can get alot of power out of those stock jugs with the right porting... also keep in mind... the more power you add your going to need a longer swinger that mean a longer chain, new chain means new sprokets, bigger motor means bigger carbs... pipes to match the motor... clutch to hold the power... list keeps getting bigger and bigger the more power your making...
also 2 grand for a crank and used cubs isnt a good deal... you can get a crank for like 400 and new cubs for like 800....
look around here for a while at the older post and get some more ideas of what all you will need before you start spending....