In my opinion, I think the reason that you're getting a better price is probably the parts cost. Many of the parts are being re-manufactured in places in Europe, such as Germany, Latvia, Czech and others.
None of the major parts in the U.S. are made here. The mechanic's labor price has a big effect as well. Especially if done at a dealership. Even a Mercedes specific independent shop, would probably charge more than a regular local shop.
You have found good mechanics, that is very fortunate!