I went through the caliber decision a couple months ago (it took me 3 months to decide!
).
I ended up with the 7mm Rem Mag because of the variety of factory ammo that would work for big game (Elk). My rifle will primarily be used for deer but I do plan to occasionally hunt elk with it and don't want to have to buy a different rifle for the few times I hunt elk. With the .30-06 most factory ammo hasfewer choices in big game loads than the 7mm Rem Mag and most of those aren't very flat shooting. The 7mm Rem Mag had more energy at 300 yards than the .30-06 and does shoot flatter and faster. The recoil isn't bad and you can add a recoil pad for $30 and then the recoil isn't bad at all.
What it came down to for me was that I had always wanted a 7mm Rem Mag so I bought one, but there isn't a giant difference between a .30-06 and a 7mm Rem Mag.
As far as a .270, most ammo manufacturers don't have any ammo in .270 rated as Class 3 (Big Game). Some people will tell you a .270 is fine for elk but if the ammunition manufacturer doesn't think enough of it to call it Class 3 ammo then I don't want to be out there shooting at Class 3 animals with it.
Federal Premium Ammunition lists 9 available choices in .270 Win - all are rated as Class 2, they list 14 choices in .30-06 with 5 of those being Class 3 and the rest Class 2, and they list 11 choices in 7mm Rem Mag with 7 of those being Class 3 and the rest Class 2.
As far as ammuntion costs, there may be some el cheapo .30-06 ammo that is $10 a box cheaper than decent 7mm Rem Mag ammo, but for most of the premium ammo there is less than $5 a box difference. I actuallyfound some el cheapo 7mm Rem Mag ammo for $16 a box (hollow points for varmints) and I haven't seen any .30-06 ammo for $6 have you?
But like others have said, a .270 Win is an EXCELLENT deer and antelope rifle. If you aren't going to be using it for Elk it will flat out reach out and touch it.
My 2 cents. Nathan