If you blow them out from the inside of the filter to the outside or use a vacuum, they can last quite awhile and get several cleanings. What kills their life is when you clean and pack dust/dirt/debris into the filter, it starts clogging similar to a AC-1 furnace filter. It then can't pull the air it needs and your engine will starve for air.
A good way to tell if your filter is getting clogged. When the engine is running pull the filter off slowly and just a little bit so there's only a small air gap . If when pulling it off slowly, there's a change in engine RPM's or extreme sucking at that minor gap, your filter is pretty clogged.
They're normally not that expensive if you shop around. I can find the inner and outer filters combined for around $30.
CA - I'm guessing that was a old stock but newly installed filter. Being a landscape contractor, he probably keeps a large stock in the shop.