One of the car mags did an extensive test of things you can do to a
car to add power starting with the least expensive and working up to
the most expensive and they did dyno tests after each addition. Bottom
line was there is nothing you can do that will make any difference
that costs less then around $300.  The air filters and all that other
simple crap is all worthless.  The least expensive but actually
effective thing you can do is to change to a less restrictive exhaust
system and you will gain around 15 to 30 hp depending on how bad the
original one was and how much noise you are willing to listen to.
They even tried adding bigger throttle bodies but without the better
exhaust they got almost no increase so taking the screen out of the
factory TB is not likely to do much.  The key is BREATHING but it has
to be a meaningful improvement.  After the better exhaust then next
thing the did that made enough difference to worry about was changing
the heads, which is hardly cheap.