The 1K for a Bushmaster is about right, depending on the model.
If you'd like some advice I'd say buy one chambered for 5.56MM NATO. It'll be stamped on the receiver. Then you can safely and confidently fire either 5.56 NATO or commercial .223 ammunition.
If you're going the AK route take the money you save over the AR and put that into ammunition and, more importantly IMO, range time.
Whatever you chose, make sure you practice, practice, practice. Get some training, too.
Most importantly have fun. Once you're confident with your rifle take a non-shooting friend to the range with you.
Good luck.
L
“Whatever you chose, make sure you practice, practice, practice. Get some training, too.”
This bears repeating. A firearm that you haven’t practiced with is almost the same as a firearm without ammo aka an expensive club. (Although this may not apply quite as much to a vet with lots of time shooting M16s transitioning to an AR, it’s still somewhat true.)