Analog and polyphon has never been cheap and the price depends on the polyphony. Each voice costs.
It’s also important to know, what the synth shall be used for. Shall it be a pad-machine or is a very flexible synth engine required, to use it many ways, from deep bass to soaring leads?
As a rule of thumb, the more flexible the engine of a polysynth is, the higher the price will be. Just check out the Modal 008 or the Schmidt as two examples.
If you want to create thick-classic-creamy pads, I would recommend to get at least 8 voices.
If you are content with the sound engine of the DM12, why not get it? A Prophet 8 could also be an alternative. Second hand prices should drop, because of the REV 2.
A most underated little box would be the VA-synth Blofeld by Waldorf. It would also give you wavetables, FM, and loads of modulation options for much less than $800. The Blofeld is very versatile and creates IMHO very good sound too.