I imagine it'll cost him about as much as he paid for his car. The 2JZGTE twin turbo engine (and subsequent accessories) is a pretty sophisticated piece of machinery. Toyota really overengineered it from the get-go and thus it's pretty expensive. The conversion isn't as simple as:
take old n/a engine out....drop new turbo engine in... It involves changing a lot of other items like the wiring harness, ecu, tranny, and so on. I know that Powerhouse Racing does this conversion so you might wanna have him check their site out for more info:
www.powerhouseracing.com In all honesty he'd be much better off just selling his n/a and buying a factory turbo car. Much less headache in the long run, but if he's really good in the shop I imagine he could pull the engine and tranny out of a wrecked JZ80 turbo and do all the work himself.