OP doesn't want to upgrade internals, so i would say get a header, either 4-2-1 or 4-1 and then continue to get the other simple bolt ons and finally get the entire setup tuned. No one here can say a full bolt on b16 tuned is even similar to a stock b16.
Sure when you add all the receipts up, its going to be quite a bit, but that's with any N/A application and if you don't have the cash to play then you really shouldn't be modding an engine. Just like upgrading your completely will be very beneficial, so will increasing the performance of an engine. You can't just get some lowering springs and a tower bar and say you have great suspension, just like you can't just grab a intake and header and say you're putting down good numbers