an air filter is an air filter. right?
 

do i get the 20 air filter or the 60 dollar one?

Depends on the car and the filter brands involved. Usually $20 will be just fine.

Cheaper filter usually has less filter media so it will allow both more air into the engine, as well as dirt.
More expensive one will have more (tighter) filter media and let less dirt and air into the engine.

So I guess it depends on how long you want to keep you engine running like new