When I first got my Sprinter we had a Mobile 1 distributor in town, and I got oil in a 5-gallon bucket from them. The cost was about 2/3 of buying in the store. Soon after that he retired and the distributor was moved to another town. Now I just get the oil at Autozone, usually three quarts at a time, in order to take advantage of the $20 loyalty point system they have.
I buy filters 10 at a time from
Europarts. They also have the oil at a decent price. Depends on shipping. Upper left hand corner under "find parts", make sure you click the correct model year.
I generally buy my fuel, engine air and cabin air filters at
GermanFilters.com or
SprinterFilters.com (same company, different names, and oddly, different pricing at times) but right now Europarts is cheaper on those filters, too, except for the heavy duty engine air filter (German Filters is $2 cheaper at the moment).