Manifold are pritty pricey but a 4-2-1 will be nice
Sportex are quite good for cat back systems I believe or cheap something like a cherry bomb and a cheap air filter will make it plenty loud.
Or if you rly wanna spend alot you could get a custom manifold place to make a 4-2-1 with a merge collectr and megaphone but then you have no cat or silencer and wouldnt be allowed on road lol