I buy Mobil 1 in 5 quart containers from Walmart for around $3.60 to $3.80 a quart. I use 6.3 quarts in my 300E.
If I bought the oil in quart sizes, it's $4.77/quart.
Walmart doesn't have the 5 qt. containers all the time so whenever they do, I usually buy at least 10 quarts. I've been worried lately that if I had too big a supply of the 15W-50, I'd get stuck with it if I bought a new Mercedes. Now that they apparently approve 15W-50 for the FSS system, I'll buy more of it when I can get a good deal.
I still do maintenance the old fashioned way and it's no big deal. The only hassle is putting that cover back on under the engine.
Of course if I got a new MB, I'd have to get a way to suck the oil out.