Ya, NADA and KBB will not give accurate values on quads, the local market will show this.
Most J-Arm banshees will be around 2K in good condition. An a-arm banshee will be over 2500 in good condition. There is very little difference in a-arm banshees through the years, so year doesn't matter too much.
If you think 1800-2500 is too much for a banshee, don't buy one. You will figure out quickly that 2500 is nothing when it comes to banshees.