NIStune boards for RB20s are only about $220 if you don't want a license for the software, $50ish for a competent electronics tech to fit it, few hundred bucks for a tune.
Don't bother with upgrading intake and exhaust manifolds, too much expense for little to no gain or as far as intake manifold goes, you will go backwards. The RB20 really needs those long runners. Stock exhaust manifold is good for up around 300rwkw too.