Dunno what the deal is, actually, but the recent AA are down to $3 each at DTPRG. While that is perhaps still a bit pricey compared to the page count (generally 12-16 pages) compared to other OSR modules, bear in mind that they are two column, not one, like a lot of OSR modules, and use fairly tiny print. Often a 16 pages adventure is pretty damn big.
And the quality is high (if you exclude the ones by Alphonso Warren, anyway), I've used more AA modules in my games than any thing else. Okay, true, I own the first 35 or so, but still, I wouldn't keep buying them if they suck (Mr. Warren notwithstanding)