crank question

hi all,
well Ive been told that i need to get a crankshaft for my kit or else it will probably end up braking, ow the kit is a 70cc Top Performance Trophy... a.k.a Black Top

which crank do u recommend me that will not be too expensive and it suitable

thanks

if thats a cast iron kit (which i think it is) i dont think u need to change the crank as its not powerfull enough/doesnt rev high enough to kill the crank