MB's just seem to be losing their value more, at least late 90's models are. You can pick up a very nice E320 in my area for $10k-$13k. My friend just bought a 1997 S320 for $11,500 that is pretty decent. The po hid a MAF problem that he got nailed for to the tune of $600.
So now it is a $12,100 car but at 72k miles thats not bad. The body has a lot of dents though and it will cost $2,500 to get it looking like new again.
Don't let those low prices fool you their are a lot of beat pos W140's out their. We looked at at least 20 cars before finding one that was decent. The nice ones are still worth a few bucks. I know a guy who owns an import car lot and he sold a mint S500 for $21,500. Late 90's flawless full service records, one owner, just had the 65k major service done, dealer maintained since day 1. It was a stunning example one of the nicest ones I have seen.
The scary part is nice W126's will be worth more then W140's in a few years. A cherry 91 560SEL will still comand $10k. Price out a cherry low mileage 350SDL, the prices on those is off the charts.