Cheapest? SKS and crate of ammo (800+ rounds) - under $500. After that, I'd go 223 (I know folks will say not big enough for deer - in a survival situation I'd even try it with a .22). There are some decent and affordable 223s out there. After that Remington 783 in 308, 30-06. I bought mine new with a 3x9 scope for under $500. It is a solid shooter and will shoot MOA or better. Plus there are tons of 308 ammo available in every sporting goods store.
THIS!
You need a common source of ammo, easy to carry, and not a cannon. I found the little .223 will do what is needed under 300 yards, I dumped my 8mm and .308. Yes I know that bigger is better but to me it's about not running out of ammo.
I will take common easy to carry ammo over uncommon bulky larger ammo.
I have an SKS and crate of ammo, and standardized to .223 and .22, that's all one needs for close encounters with game such as deer in SHTF scenarios, if hunting bigger game at longer ranges go big, but SHTF is different than hunting.
Anyone shooting extended ranges in a SHTF situation will just draw fire, far better to stay out of the open, remember their will always be a bigger gun and a better shot when it comes shooting longrange from a stationary spot.
My bolt action is .223, and out to 600 yards it will deliver a round where needed, but I intend to only shoot much closer ranges, to many variables for 1000 yard shots. My AR has a .22 rimfire kit, as why would I use a much louder centre fire round on something small?
Have .22s as well, so other than my SKS I have a common ammo supply that is much less to carry than the big bores.
Just remember this is just SHTF talk, good to be prepared just don't take it to far and dwell on something that might never happen, chill and get some relaxing trigger time in.
