UMC or Winchester White box 100rd FMJ value packs, or CCI blazer brass are probably the cheapest for practice, and can be found at Dick's or Wal-mart. While I have no first hand experience, I have heard wolf shoots fine out of the glocks, but as with most wolff ammo can be expected to be dirty. Sometimes you can also get a good deal on a case of ammo at PA gun shows, just avoid any "remanufactured" ammo, and definetely avoid cast bullets. The only other option is to upgrade to a barrel with a full supported chamber (bar-sto shoots nice), and then reload, and wit the broach cut rifling they have, you can shoot all the cheap lead bullets you want. Don't shoot lead bullets, or try to reload brass shot through the factory barrel.
Remington 180gr UMC's can be had at Bass Pro in a 200 or 250 round box. It's about as cheap as I've ever found and my Glock eats em up with no problems.
yeah, the remington stuff is cheap for practice...though i find it to be a bit inaccurate, even at shorter distances. i've been shooting more and more magtech...not expensive (by comparison that is...all ammo is getting expensive...) and seems to be cleaner and more accurate...
Edit: you can find magtech at most gun stores, i usually pick up mine at gun connection (since i've been going there to pick up several new toys as of late), but even places like ontarget will have it.