First off, don't get into a European milsurp caliber because of cheap ammo. If you do,. eventually you will be sorry.
If you get into them because you like the rifles, fine. But be warned, the days of cheap milsurp ammo are just about over. The only ones that are going to be cheap for a little longer are those produced in former communist nations.
The UN has been pushing for some time now to ban the civilian sale of European milsurp ammo, and they are pretty successful. Many nations are now simply burning excess ammo, rather than selling it on the civilian market.
Also, many of the milsurp calibers are now obsolete, and no military ammo is even being made for them (.303 Brit, 8mm Mauser, .30-06, etc), so all there is is all there is, and when its gone, there won't be any more.
Now, all of these rounds are still made as civilian ammo, but it is at sporting rifle ammo prices (as it is sporting rifle ammo), and niche rounds (not mainstream) are more expensive yet.
I do cringe when I hear of someone buying a case of 1,000 7.62 NATO for nearly $1k dollars. It's outrageous. On the other hand, gas isn't $0.70 a gallon for premium anymore, either...
All else being equal (and it almost never is) bigger bullets tend to work better.