I'd say, "just buy a .22 rifle". Anything else can come after that. .22's are cheap if you stick to the common ones and don't go high-end or exotic. You can learn to shoot with a .22. The ammo won't cost you much (current times in the US this isn't a true statement, but things will be getting back to normal soon). Typically 500 rounds will cost you less than $20. You just can't beat that for learning and having fun. Sure, by the time you get around to hunting deer (if ever) you won't be doing that with a .22. But if you ever get to that point, the time to start looking into appropriate rifles for that is when you can say "I am going to hunt deer", not when all's you can say is "I *might* hunt deer".
But you never said what you were considering sustenance hunting. If you were talking about rabbits, then a .22 is perfectly fine for that. Preferable, actually. You don't pull out your surplus Mosin-Nagant to plink at bunnies ... unless you want to have to search the next county over for the remains.
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