Looking for a 27" disk brake hard tail Med frame for my 12 year old

Hi All,
My son’s skills have surpassed his current bike. We were in Algonquin this last week riding and he really wants a new (to him) mountain bike.
We would like to find a 27’ wheels Med frame, hard tail one by, disk brake in good shape. Between $3-500. He road my Rocky Mountain for a bit, its way too big but he loved it.
Leads appreciated!