The most expensive single filter on my 7610s is the hyd filter... it is the size of a gallon paint can... and doesn't cross to anything napa can get.
Also, just a buck under that is my 'outter' air filter. It also does not cross to anything napa / carquest can get. The 'inner' filter does cross to a napa gold number.. however, the napa gold filter is only about 1.99$ less than the NH filter. Interestingly enough, I found out NH used 3 different filter canisters ont he air intake ont he 7610s.. 2 plastic of different sizes, and 1 metal. And they take different filters.. go figure. I'm guessing that one of the other filter canisters may have better matching with local suppliers..e tc.
Soundguy