MSRP for the Motorcraft 9601 air filter at FordParts.com is $19.95. Walmart sells it for a bit less. There are cheaper filters from Fram. Remove and replace on the E-series chassis is less than two minutes, although some dealers charge a minimum of 30 minutes labor for any procedure (like going to the doctor's office).
FWIW, when I get a $10 oil change at my Ford dealers quick change, the technician takes out the air filter, looks at it, puts it back in (all in hopes of selling a replacement) without charging for the labor. Job is that simple on the E-series.
I did have them put on new wipers last time in, they put on better than OEM wiper blades at a fair price, but $15 labor for a 30 second job.