The problem is that buying used as a newbie is difficult because to get the perfect bike it really helps if you have a lot of bike experience and know exactly what you need. Most bikes will need upgrades and changes, so amount saved may be negligible. End of year sales complicate this as you can get a '19 for 20% off. And the desirable steal framed mountainbike are designed to last 20, 30 years and don't depreciate the way you are expecting. They are not cars.
Here is something, a Marin Pine Mountain is essentially a Karate Monkey for less than a grand.
https://www.marinbikes.com/bikes/2019-mountain-hardtail-trail-27.5-plus-pine-mountain
And if you buy from a local shop, you will get set-up and at least a basic fitting to adjust stem, saddle, etc to make it more comfortable. You will have to pay for all these things separately if you buy outside of a shop. Plus, a lot of shops give you a discount on future purchases if you buy a bike. Sometimes for life. You can call around and see if anyone has one in stock to try in your size. Looking at the specs, I think the hubs have a cam release with thru axels. But I'm not positive. I was very tempted when I first discovered them. But I already had a KM.
https://www.marinbikes.com/find-a-dealer?near=new+york,+ny