I would have to go .308 as well and I have been considering a Savage Axis II in .308 caliber.
You can also get it in other calibers as well and it has great reviews.
It comes equipped with a scope and adjustable trigger.
You can pick one up for around $400.00 - $450.00. -
https://www.budsgunshop.com/catalog/product_info.php/products_id/90726/Firearms/Rifles/Savage/Savage+Actions/Savage+AXIS+II+XP+308+WIN+W%2FSCOPEI'm not sure if Federal Firearms carries them but I'm sure Chris can order you one.
It's not an AR platform but it can get you shooting in many calibers out of the box and for far less the cost.
The only negative review on the rifle I have seen was some people hated the synthetic stock it comes with.
I will be looking at purchasing this rifle at a later date when more $$$$ is available as I too want something with more punch and distance capability.
You can get it in 6 different calibers if you're not a fan of .308 ---
http://www.cabelas.com/product/SAVAGE-AXIS-II-XP-W-WEAVER-SCOPE-RIFLE/1849999.uts