AIM Surplus has the used Factory Glock 17 mags back in stock (they come and go) for $13.95. They say these are a mix of older manufacturings (gen2 probably) and may not be "drop-free." However... those of us that live within driving distance to Smyrna can take them and trade them in for new Gen4 mags for free.
http://www.aimsurplus.com/product.aspx?item=MGlk17