From the sound of how you might like to use it, there's nothing wrong with a commercial grade AR (chromoly lined 1:9 barrel, AR15 BCG, commercial fittings, etc). It will probably serve you very well, and the truth is many people probably gain very little from more expensive milspec designs.
Something like a $700 S&W would treat you well. And yes, it's pretty upgradeable.
Folks like the milspec rifles in part, because what you can get into for about $1000 becomes more of a "workhorse" compared to a "sporting" commercial rifle. Whether we actually work them hard or not, many of us just like to know they capable enduring that abuse.
I've got both kinds, and have enjoyed both. Go cheap, and use it as an opportunity learn what you're after before dropping the bigger bucks.
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