I think that a fair price would be somewhere between $9-13K. Maybe slightly more if you find a motivated buyer. Tire condition and if you're throwing in the usual things a first time buyer might need: water hoses, sewer hoses, leveling blocks, chocks, electrical cord/connectors make the asking price better. Those campers are often looked for because they're easy to tow and maneuver with a smaller vehicle.
2012 FunFinder X 210UDS
4-68 watt flexible panels; 1-215 glass panel/4 Battle Born LiFePO4 Deep Cycle Batteries
2014 Ford F350 6.7 Liter PowerStroke V-8 Diesel longbed, SRW