I have a 88 Acura Integra with the factory 1.6L. I was wondering what some of the cheapest mods would be to increase horsepower?

If you want real cheap(free), you could just cut your factory airbox for less restriction. If you want to spend a little money just get you a K&N filter and connect it to the factory tubing. Maybe later on you can get you a ram air or a cold air intake for a little more. Headers are a good deal for the money horsepower wise.