A new full kit from on3 is about $1,700 and the turbo "head unit" itself only cost about $300 brand new.
So, you have to remember. On a "budget" turbo kit like on3. If the turbo unit itself is only worth $300 brand new. That means it has about $1,400 in piping and all of that other crap.
The expensive part of a turbo system isn't the turbo unit itself. Its the new manifolds and exhaust system. Then start stacking your induction piping and silicon couplings on top of that. You also have to remember the waste gate..which can run north of $150-$200 by itself.
In a nut shell, figure about a $1000-$1,400 for the rest. A good place to start for the parts...call on3 performance. See if you can get the instructions from your friend. See if the instructions come with an itemized parts list. After that, start with Google.
BTW....in my opinion, if your friend wants over $150 for that head unit. I don't think its worth buying it from him.