I find a DX7 too expensive for "just" ~500€, imagine this. Just because something is rare and/or was good by its period's standards it doesn't mean it should cost this much today. Maybe I'm just being ignorant but I find FM synthesizers to be extremely overpriced for what they can actually do (I'm looking at you, Reface DX and Volca FM) and what's available plugin-wise nowadays. Sure, Dexed and a DX7 won't sound 1:1 OOB but with some EQing and maybe some saturation you can get them to sound pretty much identical imho.
With how cheap manufacturing is today Yamaha would have no problem selling "new" DX7s for cheap. But instead they prefer selling an overpriced toy that's (as far as I've heard) less capable than a Sega Genesis with an Everdrive stuck in it and a vgm player.

 

the modx is pretty damned capable. yamaha makes serious tootls as well if you look past their 'toy' market

 

well you know collectibles are high value items, no getting around the price when there were very few made and they take advantage of this, the thing I hate the most is the outrageous S&H that sellers always price gouge you on. an example of these S&H thieving sellers, I needed the small 3/8" wide x 1/2" long strat spring that goes into the tremelo arm hole to keep it from flopping around, mine fell out somewhere. I was going to order it it was $5.00 the f*cking b*st*rd wanted $54.95 for S&H within the same country, USA, it could fit into the end of a very small envelope, weighs almost nothing. I didn't order it, instead I found a spring at a hardware store for 15 cents, had to cut it shorter and sand it smooth at one end, and it works perfectly.