So what kind of prices should I pay for either in general? I know the more rare ones cost more. I’m looking more for a baseline

Baseline?

You can get a good condition USGI M1 Carbine made by one of the more common manufacturers for around $800-$1000. They go up from there, based on rarity and condition.

Service Grade M1 Garands from the CMP are $750 shipped.

Thanks, I was thinking about the cmp, seems pretty easy to join

Depends on the range you're going to be shooting it at. If just 100 yards or less, I'd go with the carbine. If you see yourself shooting further out, buy a Garand. Perhaps the best thing is to find a place or someone that has both and shoulder them and see what feels better to you. For me, I'd rather have a carbine.