.308 or 7.62x51. These would be a good start. I did see win. 7.62x51 in the May MidSouth Shooter Flyer. 200rd for $99.99 Another good placs to find ammo is at the gun shows. I do know that for some types of mil. ammunition the price has gone out the roof. 7.62x51 LC for example.
I went to that AbleAmmo site and looked at .45 stuff. A good selection and the prices weren't bad. However, if you are just wanting some range ammo for practice, I use the CCI Blazer .45 230 gr. FMJ. 50 rounds per box. AbleAmmo.com had them for $15.35 plus whatever shipping was, but Wally World ( ) has them for around $9.57 a box. They sell the Winchester loads of 100 round boxes for about $22.00 or so. My wife works there, and I get the 10% employee discount, so I get a pretty good deal on good stuff. Some of the Supercenters don't carry guns anymore, but even some of them have ammo. And they have a pretty decent selections of handgun, rifle and shotgun ammo at the 3 here in Mobile.
Be careful of the discount stuff you will find at a gun show. I bought 100 rounds of reloads from a dealer for $15. It was not FMJ, just lead. I shot them up in an indoor range and after I had shot 4 shots of my eight a clip, I had a cloud of smoke around me that I had to wait for a minute to let the smoke dissipate to acquire the target to sight and shoot! And I don't know how many patches I used in my barrel in cleaning it to come out clean!! It was filthy!! Never again!!