Lets not go over the top here if he just wants a power figure.
Simon Natalotto over here did 638rwhp (472rwkw) and 131mph to back it up, with a 5u block, built 2.6L + t04z, standard box (albeit he's broken a few), and standard driveline (as far as I'm aware).
Basic's would be a well built std capacity motor (allow 13-15k), fuel system (2k), single turbo (4k), and a decent clutch (1.5k).
Thats assuming all the basic mods like exhaust, cooler, power fc, etc etc are already done.
Still a long way off from fitting it into a 20k budget including labour though...