$22K is definitely ball park. Be aware tho that these undriven, like-new cars are old. So old bushings, old hoses, etc. And lack of use is not necessarily good for wheel bearings, engine, etc., etc. My ideal used Caterham is one that has been used and maintained regularly, more than low mileage. Still, I think the price is reasonable if it's in as-advertised condition.
Other thots: the Dedion rear is a plus, ditto long cockpit. Is it 5sp., 4sp or 5sp, LSD, leather seats, weather package (top, heater etc.), standard roll-over bar or FIA bar?
My 1st Caterham was spec'd like yours and I loved every minute of it (after I replaced tires, hoses, engine mounts, -you get the idea). I put 15k miles of combined street/track use on it and a smile never left my face.