IF your friend is an honest, reliable guy, i would look into it more. if its a shop that does this regularly, they may have extra parts, or get parts for cheaper than retail. and if its HIS shop, he may be throwing a friendly discount your way
if not, i would steer clear. 700 dollars wouldn't forge the internals of Power Wheels toy truck.
Can you provide more details on this. 700 for labour maybe ...but with the parts as well ...doubtful. unless hes somehow getting the parts for free or has spare sets lying around ...lol...anyways provide more details on the background behind this and explain your pricing so that it adds up in everyone else's heads