I just had this done and the cost at an independent was $1686. This included spark plugs, by pass hose and temp switch.

At a dealer of course, it is much much more.

Although I caught the oil in the coolant early, the tech said it was very minor so far (some cars come in with a 1/2" of oil floating), he said that doing the work ASAP was important as oil causes premature failure of rubber cooling hoses.

glenmore
1991 300CE
1990 LS400