96 s320 new to me, first time Mercedes owner.

Immediate need will be to reset my airbag dash light after I replace the battery. Knowing this is only the beginning of a long and intricate relationship with this car, I want to get a scanner that will keep me headed in the right direction for repairs, many of which I will tackle myself. My wife's car is a Toyota, and I have a Chrysler van, a Subaru Forester, and a couple of Chevies in the family. It would be good, if I can find a diagnostic device that is multi-vehicle as well as multi-functional. I read a reference to a unit in the $150 range that is specific to Mercedes. I don't recall the date of the reference, but change is so rapid in electronics! I expect there should be a device for up to a 100 more that would provide most of what I seem to need. All thoughts appreciated .