If your looking for accuracy, reliability and durability, your looking in the 600-800$ range
G&P M16A3 would be the best platform for that, I'd say typically around 600 or 550 at the lowest for the AEG itself (new), but they're tanks.
Beneath that, classic army, you can get a good starter package (gun, mags, batteries) for 500-600
But +1 on the PTW being the best you can buy for an M16A3, but yeah, EXPENSIVE
And please don't think we're trying to push expensive guns on you, but with your given criteria, and our years of experience, these are your best options. Doesn't mean you HAVE to buy one, it's just the best choice for what your looking for.
If your looking for cheaper, as was stated, G&G is probably your best option. Personally I hate their weak metal bodies, but it's not like you look at them wrong and they explode lol
Their internals are not bad, and of course, you can always upgrade it to be way better down the road!