I truly believe I am driving the finest production car ever built, the 1990 300SE. As with most S-Class, the folks who buy them new can usually afford to take care of them properly, as was the case with my car. The car has a quiet cabin, and a wonderful ride both in town and especially on the road. It would be hard for an 'established' person to find a better car or a better overall value. It is also one of the safest cars ever made.
After 1991 ALL of the luxury brands added oodles of electronic gadgets which are sure to fail and expensive to repair. While my car has airbags and ABS, the only "electronic" features I was compelled to add were a CD player and keyless entry. One of my favorite stock features of the S-Class is it's practically unnoticeable rear defroster elements. Other than while they are quickly defrosting your window, they are virtually transparent.
I average 17.5mpg overall, but-knock on wood- have had very little to fix in three years of ownership. I will be replacing the tires soon though. You will get a safe car discount on your insurance and you can buy a REALLY nice one, after a patient shopping period, for under $5000. Trust me, hold out for a nice one and you will save money as you will have little to fix upon gaining ownership. One flaw this is common to see on this vintage is a non-functioning A/C. For me in the PNW, it is not a problem for it to be non-functioning, but in warmer climates you should know that fixing it can run $2500.
They are so well built that I expect to drive mine the rest of my life, I am in my forties, and I tell my friends it will be my coffin as well when I die. Sure I may spend 3000 on an engine one day, and the same on a transmission one day but isn't it nice to own a 18 year old car that such repairs are 'investments' rather than good money after bad. Some folks have gotten 1,000,000 miles on the W126 chassis which includes the 300SE. Now THAT is a fine machine, and in the long-run it has to be greener than the ten ordinary cars it would take to go a million miles!