The car would have to be in truly exceptional condition to get anywhere near any of those prices IMO. Unfortunately W215 CLs have a reputation as a money pit both in terms of running costs and repairs. The relatively few 600s on Autotrader, Pistonheads, etc are generally priced much lower.
You might do OK though as your car is very low mileage. But I think it would need to be a facelift model (easy to tell as these have a widescreen satnav).
I agree with Bernard. You get what you pay for. Lower priced cars are probably in need of some fairly expensive work. On all W215's the ABC suspension is a concern & with the 600BT there's the added cost of coil packs which generally seem to require replacement after 60-70k miles. There's one on each side dealing with 12 of the cars 24 spark plugs so it isn't cheap. By way of example mine had some ABC work done and the packs replaced shortly before I bought it which cost the dealer 3k. Since then I've replaced the water pump, radiator, AC condenser & tyres (admittedly those issues could happen to anyone - I'm just saying you need to go in with your eyes open). The fun factor can't be overlooked though - the torque this thing has blasts you past pretty much anything. A road you've travelled every day which you previously regarded as having four or five overtaking opportunities, in one of these suddenly has twenty ....
Easy mistake to make. Basically the 600 went Bi-Turbo the same time as the 55 AMG sprouted a supercharger taking both of them into the 500 bhp club. To go with it, the 55 got 519 lb ft torque and the 600 got 590 lb ft.
Personally I wouldn't touch with a barge pole the pre-facelift versions, especially the 5.8 litre 600 (the later bi-turbo is actually 5.5 litres, same as the 55 AMG). That strange engine with its fancy cylinder shutdown system is known to be problematic.
As a final note, regarding the COMAND system, remember there were two widescreen versions fitted in the facelift cars, the first of which was pretty much unique for the 2003 model year featuring a visible CD slot above the screen.