Not the cheapest but in stock (at least they were) & lower than everywhere else.
Ammo To Go : 1 - Magpul PMAG P30 Gen M2 AR15/M16 Black 30rd. Magazine [MAG571BLK] - $19.95
Just saw Kentucky Gun Co has Magpul 30rd gen M2 - black - for $14.95 each in stock
http://www.kygunco.com/magpul-pmag-30rd-arm4-gen-m2-moe-magazine-black-no-window-5762
Ammo To Go : 1 - Magpul PMAG P30 Gen M2 AR15/M16 Black 30rd. Magazine [MAG571BLK] - $19.95
Just saw Kentucky Gun Co has Magpul 30rd gen M2 - black - for $14.95 each in stock
http://www.kygunco.com/magpul-pmag-30rd-arm4-gen-m2-moe-magazine-black-no-window-5762