I'd add especially when buying used in good condition. A D700 for example goes for around 300 bucks. And that is a truely professional DSLR, the smaller sensor actually doesn't matter if you don't plan to prind barn door sized and then brake out a microscope. Back the day, it was Nikon's low light king (obviously not anymore) and basically the same camera as a D3. So still plenty good for ethusiasts and amateurs. For difference to a Z6 you get a lot of good glass (always a better investment than camera bodies) and there should still be some money left over to go to exotic and beautiful places to actually take pictures. If you want more resolution, a D750 goes for a little over double a D700 and a D800 can be had for around 500.

If you earn your living through photography, things are of course different.