anything used to make it faster/have more power is going to impact your fuel economy. if you are not super concerned with that open up your intake and exhaust. both are inexpensive things you can do yourself if you can weld. intake you can do without welding if you use aluminum piping and silicone couplers. keep in mind the colder the air the more power. aluminum will regardless of its great heat dissipating abilities still become heat soaked after a while. best way to combat that is to have it ceramic coated. aside from those things other inexpensive mods for power would be to gasket port your heads, exhaust manifolds, intake manifold, and open up/polish your throttle body. dont expect a ton of power but it will help. the more efficient the air can flow the better off you will be. all of this can be done on the cheap with just a little bit of time (except for the ceramic coating, that you will want to drop off and have done by a professional. average rates for that are going to be $12-$15 a foot plus .25hr blasting). if you want to step things up while you are there and you have your manifolds off you can have those ceramic coated as well. i have had great luck coating everything i build.
if you have fabrication skills you could build yourself your own eaton supercharger setup. they are really quite inexpensive if you know where to look, another choice would be a pair of small turbos (they can be just as effective or better than a supercharger if you size them correctly and know what you are doing. they will atomize the air when you are in vacuum will help with your fuel economy).
another option is to doing timing adjustments. advancing or retarding your timing can/has great effects on your power band.
you can cool your fuel with an ice box as well.
there are tons of options to make more power on a budget. like i said though, keep in mind regardless of what you do, your fuel economy will suffer. any unneeded weight you can shed will help, like switching to a lightweight battery that puts out equal power, running lighter wheels or tires, ditching your back seat if you dont need it, never driving with more than half a tank of fuel, etc. also keep your engine maintained, poor maintenance will do nothing but hurt. keep your injectors and valves clean, regular air filter cleaning/replacement, spark plug changes, even seafoaming every few months to clean up the carbon buildup will do wonders.