DX7s don't go for a high price. The market is flooded with them. If you pay more than $600, you paid too much. You can easily find one in the $400 range.
It's a 40 years old digital synth (so trivial to replicate one to one), with no special hands on controls as a keyboard, and one with 150,000+ units sold, with about a dozen modern replications.
$400 would already be an impressive sum for such constraints.
But it regularly goes for 800+ in Reverb.com for example.
Good luck finding a 60-key MIDI controller with velocity-sensitivity and aftertouch for less than $200, and it's without getting into replication (of either the controller or the synth).
