You aren’t going to find an AK for cheap. Guess it depends what cheap means though. For a solid AK I would personally budget 1k as a starting point.
as for the AR, piece together something from PSA. Just saw an email from them and you can piece together and upper and lower for $400 not including transfer. Throw a mag lock on it. The cheapest way to go. Personally, unless a range toy, I would shy away from mag locks.