With only $700 I'd say that NOS is the only way to go - for a guaranteed victory.
But
Hammer -- 15s
I've bone stock GTs pull deep into the 14s and the lightly modded GTs (gears,exhaust and pulley set) low 14s.
The exhaust pulleys and gears would be a good investment too. Because if he loses he will have some ofthe necessary mods completed already.
Either way ... good hunting.