AR's are cool and I had one in the Marines, but too much maintenance, and expensive. I dont like the m&p15 sport missing the dust cover and forward assist.
Good ones are available in the price range you set, so let's go ahead and cross off the 'expensive' disqualifier.
As far as the forward assist goes, I don't know that I've ever seen anyone legitimately use one. Aside from maybe being down to your very last round, and it won't quite chamber properly, what situation is the forward assist supposed to help with?
Dust cover is a nice feature, but does it really offer much functional protection for the rifle's internals? The bolt carrier group already blocks off the ejection port quite handily, and there aren't any situations I can think of where you would want to lock your bolt to the rear and then close the dustcover. Besides, the AR has a nice closed-top receiver anyway, so debris large enough to really wreak havoc can't get in there anyway unless you've got the bolt locked open.
I honestly don't think I've noticed any special amount of maintenance with the AR platform, I mean you scrub the bolt carrier group down every few hundred rounds or full day of heavy shooting, run a bore snake through it a couple of times, leave it lightly oiled, give it a squirt of lube or use some dry lube before putting a ton of rounds through it, and it works perfectly.
Service rifles choke because the mags we use for training are often nearing the end of their useful lives, not because the rifle itself is unreliable. Use Pmags or any decent mag in good condition and you bascially never see feeding problems with them.
That said, it does sound like you are more looking for a deer rifle that could be pressed into additional service as a fighting rifle if absolutely needed. There are lots of cartridges the AR can be chambered in that fit that role well, like the 6.8 or even the .30 Remington AR, but you would probably do better with a .30-30 lever action or an SKS or Saiga in 7.62x39mm, for cheaper ammunition.
I'd say if you want a rifle that can grow with you, an AR would be great, cheap and plentiful ammunition, loaded with one of the many non-varmint bullets it will work on deer, and in the future you can buy a more hunting-specific upper to more fully match what you want your rifle to be capable of. But with the price and guidelines you've set out, right now the other rifles are probably a better match for you.