Colin, you need to ask this question in the W210 forum - not the For Sale/Wanted forum (W210 is the chassis identification for the car you are looking at). Ask this question to owners of similar cars and they will give you the best answer. Personally, for that mileage, I would estimate $2,500 to $3,000 for a W210 with 260k miles. Since he is the original owner, I hope he has reams of service documents to show the car has been well maintained.
You need to spend many hours on the W210 forum asking about the strengths and weak spots on these cars and what are the costly repairs that (hopefully) have been done. Please understand, repair parts (particularly OEM Mercedes parts) are expensive as are labor rates. If the car has not been maintained (especially over the past 100k miles), you could be looking at significant repairs that are needed that would greatly increase the investment you have in the car. If you have to immediately dump $3,000 in repairs into the car, you would probably be better off finding a similar car with 80k miles on it for the same total price.
I also strongly recommend a pre-purchase inspection of the car by an independent MB workshop (also called an "indie") - have the car examined for $100 or so. The owner should have no issue with you having the car examined. A good indie shop in Atlanta is Blue Ridge Mercedes (Jonathan):
Here is the link to the W210 Forum:
W210 E-Class - Benzworld.org - Mercedes-Benz Discussion Forum
1984 W126 500SEL Fully Documented AMG -5.4L, Sebring exhaust, full suspension, 2.82 LSD, 8"/9" wheels, spoilers/skirts, Recaros, door wood, Clarion rack stereo, speedometer. Anthracite Grey 172, Black Interior
1990 560SEC AMG - 6.0L, Sebring, suspension, 2.65 diff. Arctic White/Blue
1994 E500, Polar White/Grey
1990 560SEC, Black Pearl/Black (Japan)
1991 560SEC, Black/Palomino
1961 W111 220SEb Coupe
1987 W126 560SEC
1995 W124 E420
1996 R129 SL320
Last edited by alydon; 08-21-2011 at 05:18 AM.