I'd start building the foundation for a better setup. Any aluminum head swap with can intake etc is going to devour more than your budget.
I'd make sure you have a full exhaust in place, all 2.5 inch. I prefer bassani, because it's all high quality.
For headers I like equals, me personally I think long tubes are one of the most over rated mods to a 302. Say what you want, I know guys with stock 302 shortblocks that make around 350rwhp NA and 500rwhp aspirated with them so i don't see where the restriction is. Maybe on a 347 or 408, if you are doing that, headers are the least of your worry so...
The cam with stock heads is worthless, be even more worthless if you float valves.
Little things add up, so right now do the basics and make sure the
suspension is good and the car runs right while getting your finances in order.