Go to Walmart or any other chain store that sells ammo. Look at .270 Win, .30-06, .243 Win, and .308. See not only the availability, but also look at the price for basic ammo like Federal Power-Shok, Winchester, and Remington Core-lockt.
Then look at the same ammo in .25-06, 7mm-08, and many other great cartridges. You will see the first batch going for $18-22 a box of 20. The later group for the same kind of ammo runs $28-32 a box. I know, it's crazy that a .25-06 is just a necked down .30-06, (as is the .270 and a few others). The 7mm-08 is a necked down .308. Yet, they cost more for the same type loadings.
It's pretty much a matter of sales volume and how long the first cartridges have been around. There are just massively more sales of .30-06 Springfield, .270 Win, .308 Win, and .243 Win made each year versus the others. The other rounds are excellent and no reflection on them. It's just that the volume of sales keeps the classics less expensive and more likely to be found anywhere that sells ammo.
During the last ammo panic I noticed that those first classic (not that some of the others aren't now) cartridges were the last to leave the shelves and some of the first to return.
I personally find a nice, bolt action .270 Win to be an excellent all around rifle unless you are going to focus heavily on moose, large elk, and grizzlies. Does't sound like you mean to do that though. A .270 shoots flat enough, hits hard enough, and is still comfortable enough in a well set up bolt gun, that you can shoot it for pleasure and to get game. You can still use a 130 grain bullet for varmints if you wish and it will handle the wind better than a .223 or similar. Might be a little overkill for ground squirrels though.
There is also no reason you can't shoot the first four over distance. Any of them will let you do target work at 500 yards. You may not be shooting like a precision specific rifle, but then you need a precision rifle and experience to shoot "precision" rifle regardless of caliber. You can however, learn to shoot and hit quite well on reasonable targets with a good bolt gun and any of the first cartridges I mentioned.
Remember, sniper rifles in major world conflicts were simply service rifles that showed a bit better accuracy and were scoped. Men were hitting other men in conflict out to 500 yards or a little better with these rifles in .303 Brit, 8 (7.92)X57mm Mauser, .30-06 Springfield, and 7.62X54R. The .308 Win/7.62 NATO has been a standard sniper rifle for a long time and the military still has plenty of the M24 and M40 sniper rifles in .308. Even with the new darlings of .300 Win Mag and .338 Lapua, the .308s still see plenty of action.
I've seen plenty of folks jump on a .300 Win Mag for their first rifle. They take it once or twice and decide it's not for them. Too much recoil, muzzle blast, and too expensive to shoot. They develop a flinch and can't group at 100 yards, let alone beyond. Granted, some folks can jump on one and take right to it, but for too many it's just too much for the first rifle. Even a .30-06 is too much for some people.
I'd say go with a .270 Win or a .243 Win (and I can't even stand .243 for my own reasons.) Go with a decent scope. Then use the rest of your money and get the best bang for your buck by learning and practicing with the basic spend around
$18-20 for .270 Win instead of
$31-50 for the magnums. You will get more practice, less blast and flinch, and be quite capable in the field.
As others have said, a bolt gun isn't really a good defense gun. If you have to reach out that far then it really isn't defense under pretty much most jurisdictions. For close range, it pretty much sucks.
If you want to use a sporting type rifle for defense, then a Marlin 336 or Winchester 94 (those you need to find used) in .30-30 Win or one of the win 92 clones or a Marlin 1984 in .357 Mag, .44 Mag, or .45 Colt will serve you well with quick handling, more rounds on tap, usually 6 in the tube on a standard .30-30 and 8-10 in the revolver cartridge lever guns. You can also top off the tube mag round at a time as you go like you would a pump or semi-auto shotgun.
Lastly, you might consider a Browning BLR in .223, .22-250, .243, or .308. It's kind of a bolt gun that operates with a lever. Slim, fast handling, and uses a detachable, albeit small round count, magazine. One of the guns I really wish I had back was a BLR 81 in .223. Great shooting little gun and sweet handling.
