Yeah, I kinda thought, that for the purposes of this discussion, we were being asked to recommend calibers that would not only be suited to the purpose, but could also be expected to easily find ammo for at the most reasonable prices. If I got that right, then we are doing a dis-service to recommend some of the calibers that are being mentioned here. It seems to me that the only calibers that meet this criteria are 243 Winchester, 270 Winchester, 308 Winchester, and 30-'06 Springfield. While there are other calibers that will perform just as well as these; they really don't belong in this discussion since they will be but poorly represented on the shelves of most places out in the country, if at all, and when you do see them, they cost half-again more. It doesn't matter if the 6mm Remington. 25-06, 280 Remington, or what have you, is your darling cartridge. Those are not competitively priced on the shelves and are less well represented.
There is a wide selection of plain hunting ammo for 243 Winchester, 270 Winchester, 308 Winchester, and 30-'06 Springfield, and it all is priced about the same. Premium ammo is available as well, but we were talking about budget ammo. If recoil is an issue, and pronghorn is the major focus, then the 243 is the stand-out winner. Otherwise, take your pick between 270 or 30-'06. 308 Winchester would be a modestly respectable option.
It seems unreasonable to look at this much differently....