First, the OEM exhaust is really really quiet. you barely hear a thing below 4k rpm.
Second, Try to replace either the HFC or Short tail to see if that is loud enough for you. I added both to my 370z and it was too loud like a V12!
my current set up is HFC + invidia gemini and imo it is a good combination of sound and noise level. But that would cause round 1.5 grand in total.
If you are on a budget, try the short tail first