The 450SEL 6.9 was and is one of the best performers ever to come out of Stuttgart. I currently own two of them myself, one with a mere 47K behind it and another with a whopping 203K on it! I see you're looking at one of these land rockets, so I'll do my best to help you out..
There are a few things to check out on 6.9s (and other W116 chassis MBs) before purchase.
1. IMPORTANT! Check condition of stabilizer bar mounts at firewall!! Driver's side is under brake booster and passenger side is under windshield washer resirvoir. You have to look up into the wheelwell towards the upper-inner corner of each front tire, in there you'll see a rubber donut, which serves as the connection from the stabilizer bar to the torsion bar. Make absolutely sure the metal around this rubber bushing (one in each front wheelhouse) is nice and solid. I suspect that if it is a CA car, you won't have many problems with rust, but check to be sure, as the car may have been wrecked.
2. Check operation of hydropneumatic suspension system. The car should sit level front and rear. If the front is lower than the rear, start the car up, let it run for about 5 minutes, then hold the throttle @ 2,500rpm for 1 minute. The front end should then level itself out. If the light on the dashboard is on, then the system is not generating enough pressure in the central resirvoir and is in need of repair. Either a bad pump or bad main valve are the two most common culprits.
3. Check operation of climate control system (this applies to all 116s). These early generation systems were extremely trouble-prone, so make sure all the A/C needs is just a freon charge!
Basically, you have to go over the entire car and make sure it is structurally and mechanically sound. Pay a good shop for about three hours of labor (what I charge) and have the car gone over front to back. If there's any MB to have inspected before purchase, it's a 6.3 or a 6.9! $9,000 seems like a fair price for a 92,000 mile car. And as far as maintenance, as long as you drive the car and exercise it regularly, the maintenance shouldn't be any more than any given MB--although 13 quarts of oil for each oil change can get a little pricey! But the engine and drivetrain are extremely bulletproof, so if the car checks out well, then by all means go for it and enjoy life in the fast lane! Welcome to M-100 mania!
'93 300E 2.8