Fair price will very a bit, I paid $9500 for mine two years ago used, but every bell and whistle was ticked off the list; bashplate, Wings Exhaust, folding mirrors, risers... It was in immaculate condition, not so much so now

Far as things to watch for, there are very few:
- likes to be topped up with oil, as the cam chain tensioner is hydraulic based on oil pressure.
- the like to be warmed up to two bars before they are ridden
- wiring harness can be a bit taunt an wear
- get an extruded gas cap if it doesn't have on already. The KTM one for this generation is just a funnel for dirt to ride into the tank.
- check the sub-frame bolt, these break occasionally. Just pull the of the bike up by the grab rails, and if there's more than about a 1/4 inch flex then it's broke. Rally Raid Products UK has stronger replacement ones on offer:
http://www.rally-raidproducts.co.uk/products/Subframe_Tank_Mounts
- headlight is just weak, eat lots of carrots
Still, baring an issue I had with my Rally Raid tanks stressing the connector to the regulator rectifier, this is one of the most reliable motorcycles I've owned. Freaking adore the beast.