Fyi you don't need an engine rebuild before supercharging, ...or turbo charging either for that matter (depending on the BHP of course).
If you did decide though that you wanted a forged engine build followed by supercharging then you're going to be looking at some serious expense. Maybe £15K or even £20K.
If you want a break down of the prices I paid and the parts I used for my 350Z supercharger build just send me a PM & I'll give you the list. Will give you an idea then of a supercharger build costs at least then.
If you want some costs, info on an engine build then maybe try asking TT350 or zmanalex.