Under $100, that would give you a cooler which is quite powerful!
Lets see... If you friend is serious overclocker then i would say:
Thermalright Venomous-X costs around $60.
If he just wants cooling and moderate overclocker then: CM Hyper 212+ would be also good at around $30.
but I think those are just to big for his case
Which case does he have?
His case is big enough he'll just have to lose his side fan. Losing a side fan is an easy sacrifice for improved cpu cooling. Just find a 212+ and lose the side fan. 212+ improved temps by at least 10C side fan 2-3C.
Sorry i didn't notice the cabinet mentioned. I checked the specification mentioned for the NZXT Tempest and it is only 2mm short of my CM690. So i would say it should fit easily. I have the True Black 120 Rev. C and it fits easily with one 120mm side fan. No problems!