If you use 1000ft/lbs as the amount of energy you need to take down a deer, a 223 bullet in the 70gr range will have that energy out to around 200yards.
At around 200yards a 75gr 223 bullet will have more energy than a 150gr 30-30 bullet
..... just make sure the gun will feed and stabilize a bullet that long.
My thought is still "Happiness is having enough."
A lefty bolt gun off a consignment rack in .243WIN or bigger would likely be considerably less than the cost of a new Levergun ..... and offer much better ballistics and terminal energy. It would certainly be less than 1/2 the cost of a suitable AR at current prices.
For what AR's are running, you could buy a reloading set-up and a lifetime supply of components.