Where can you find factory Glock mags for under 20 bucks? I'd certainly pay the difference if I can find them for that price.
Edit: Here is a great price on the Magpuls, with FREE SHIPPING! I dont' see anywhere at PrimaryArms where shipping is free, so unless you order a bunch of them, this price is probably as good or better than the original post. They are $15.15 at AIM Surplus, and being in Ohio, I usually get stuff from them within a couple days.
You can get them close to that. AIM surplus, GTDist.com have them for $21.95 typically before shipping. AIM can often be out of stock on many of the calibers. Botach with their volume discount (15% off Glock mags when you buy 5 or more) usually has them close to $20 with free shipping.