$50-75 is real tight to work with and not really enough to make a difference. I used to buy into those "HP increase" gadgets and installed a few on my jeep, but unless you do anything major: supercharger, turbo, engine overhaul,piston/cylinder work etc, you aren't going to feel any difference with just a few gadgets and much less for anything in the $50-75 range. I have currently installed the following on my jeep: AEM cold air intake ($200), 62mm throttle body (~$60), throttle body spacer (~$40), Banks header and cat back monster exhaust ($400), Random Tech high flow cat (~$150), all those upgrades came with hp/torque increase claims and increased mpg claims and in the end, i think i netted 1-2mpg better (that was really the AEM more than anything) and prob picked up 10 hp if that. Trust me, you won't feel ANY difference and it's all mostly a waste of money. All those products seem to work well on the 6cyl as i have friends who run a combo of all of those and their engines seem to do much better, but that may be due to the larger displacement and power available to them. If you want more power out of that 4banger you're going to have to turbo, supercharge or other heavy engine mods, and of course you can top it off with the parts i listed above. Cheapest and most financially effective way to regain that power loss is probably to regear. By that I mean even though it costs more to regear front and rear axles than it does to buy all the stuff i listed, you will actually gain something from it.
