In my opinion the best bang for the buck you're going to get while still keeping the price point low is the Ruger MPR. It comes with a 15" mlok rail, a 18" barrel with a comp, and rifle length gas. It also comes out of the box with magpul furniture and a good 2 stage trigger. I don't think you can find anything close to as good out of the box for anywhere near that $$$. I'm not sure about now but you could get them for well under $600, I think about $560ish.
Yep. Happy with mine.
https://www.sportsmansoutdoorsuperstore.com/products2.cfm/ID/199005