well, a checkup would technically be different from a service. a checkup to me would be you take it in, they look at it, and tell you what it needs. a 100k SERVICE is major. think of it as a replace-everything-on-the-motor service. then, there is other stuff, like brakes. suspension. a/c. all fluids. o2 sensors. some places, like the dealer, will just yank out a list, and say, ok, you need this, this, this, yada, yada. a good shop will probably actually LOOK at the items, and tell you if they think you should replace them. take brakes, for instance. a good shop will look at the rotors and pads, and tell you if they need replacing, or it can go for a bit more. this is why it helps to take it someplace where they actually work on a lot of these cars. they will be more familiar with what goes wrong. a 100k service is gonna cost a lot, because there is a lot of stuff to change.