Car HP Increase questions?

1- If the engine is stock then a factory air filter allows almost twice the air through than the engine can ever use. It also is designed to stabilize the airflow through the MAF sensor and allow better control of the air/fuel mix. It is also designed to pull in clean colder air from a place outside the engine compartment, unlike most of the "cold air intakes" on the market that put an open filter under the hood. 2- These days a simple tune up of oil change, new plugs, cleaning the throttle body, will cost that amount of money. You might see intakes, tuner chips and more that claim increases, but most of them either reduce the power, or they trick the computer into thinking it's colder than it actually is. That triggers the ECM to add extra fuel to the mix, however that only decreases your mpg without adding any actual power increase. The only true way to add power is to build the engine for it. For instance adding a turbocharger, however you also need to build that engine to handle the extra power. Many don't do that and end up walking because they broke something. It's also why one of the first things I tell people is, don't modify your daily driver with unknowns. Better tires, cosmetics are OK to an extent. But buying a $200.00 "Universal turbocharger" kit is just about always a waste of money.

These are the filters. They were only like $20 each.

Just put a good filter in the factory box. If you actually test the filters like K&N or Spectre oiled gauze filters you will find that yes, they do flow air faster than a standard filter, but they do this by having larger holes through the material. The oil is supposed to capture the dirt and dust, but it doesn't work that way in actual use because there are still larger holes in the filter where there is no oil. The factory airbox actually does a much better job at filtration and keeping water out as well as removing engine drone and helping the engines control systems operate properly.

I was doing this for horsepower increase.

Won't do anything at all to increase HP. In fact it can decrease it because it can introduce turbulence in the airstream that causes an odd flow over the MAF.