While classic airmail covers still fetch high prices, it is worth noting that there hasn't been any real airmail action in quite some time. In fact, the last formal USPS airmail route serves about 20 customers living in the 2 million acre area in proximity to the "River of No Return," actually the Salmon River of Idaho. That's a lot of territory to cover for not a lot of customers, who were going to have their last delivery in 2009 until the Idaho congress stepped in and convinced the PMG to keep delivering to the remote outposts.
The plane service offered by the USPS cost them $44 per customer per week, a price that a cash strapped postal service could ill-afford, even back in 2009. In the intervening years the postal service has closed down many rural post offices, protested by many residents who claimed the PO's were also popular town meeting centers.
There has, in fact, been an uptick in prices, outpacing inflation, for classic first flight route covers up for sale in recent years. I hope there is a collector living along the River of No Return saving his mail. With only twenty people living along the route, every letter and bill is a potential airmail rarity. Or at least it's nice to think so.