Bit late to the party, but here it is anyways - such a camper is basically worth whatever it's worth to you. It's a matter of supply and demand more than anything - most campers tend to be designed for max comfort in fairly easy-to-access locations and as such are not well suited for routes that takes advantage of flexy suspension and actual use of 4x4, newer offroad-friendly campers can cost as much as the truck that carries them, so many are looking at the older models but again them not being all that common tends to drive up prices of units in good condition. So basically you should look around on CL and maybe ebay and see how the price of that particular camper compares to other similar ones. Also, keep track of condition of appliances - the LP furnace is usually not too bad to bring back to life if it's DOA, but an absorption fridge like the one in that Lance will set you back at least several hundred to have repaired, more if it needs replacing.
And don't forget to factor in the cost of the means for attaching the camper to your truck - spring-loaded frame-mounted tie-downs are the best if you plan on leaving the paved roads but they are not cheap, stake-pocket brackets with chains are cheap but also a good way to damage your bed if you crank them down too tight and then go test the torsional stiffness of your frame.