What has been done to the car?
Open Cone/conical Air filter(any good K&N type will do) Spectre filters are good at a good price.I would lean you towards AEM dryflow, I had most others but staying with AEM from now on.
Make your wastegate adjustable if not already.
Tune up....Plugs and wires atleast. NGK V power plugs or good Delco set, I use NGKs. Wires, autozone duralast brand works just fine, same as my taylors or order some taylors from summit.
If you got a good exhaust system (no rust/rot pipes) a set of Turbo mufflers would be great. summit, dynomax, even cheap autostore brand would be ok. (turbo mufflers,no flowmasters)
A universal hi flow cat would help also. Depending if you got alot of miles on your stock one. Most hollow them out but, three factors I don't like about that. 1. it affects flow/sound of exhaust, 2. bad for earth. 3 hp gain isn't that much more then Hi flow unit of today's tech.
Electric fan Convert, Ford 17'' Taurus fan or Lincoln/Mercury 18'' Fan would be great,cools even Big Blocks with ease. or atleast Flex Fan with spacer.
That's as cheap as it's gonna get,or that I can think of..... then addiction sets in.