Prices vary greatly; state, community bought from, condition, etc.
In general:
Dk 500-1500 depending on condition, location, prestige, and selling venue
Dkjr 200-750 (same as above) they made way more of these than dk
Dk3 200-750 (same) made even more of these.
The dk and dk Jr both use the old Nintendo wiring, literally just swap pcbs at will, same monitor and control panel. Dk3 used a different wiring scheme (edge connector) and the monitor actually has different wiring (# of wires), you can run a dk or Jr PCB from the edge connectors, so the dk3 cab with edge connector wiring is fully, reverse-compatible with older vertical nintendo pcbs. To play dk3 on a dk or Jr cab, you would need to rewire for an edge connector setup, or just get an adaptor and rig the player 2 start as a fire button.