I'm not too familiar with the wagons ("sport combis") or any of the six-cylinder incarnations of Saabs.
I can give you some general advice, though. Saab... they're not in business anymore. Lol And obviously you know that, so just go ahead and find a real good shop that specializes in Saabs, Swedish cars, or European cars. Do this before you buy the car so that you know where to send it should anything ever go awry...
At 100,000 miles... general maintenance like spark plugs, filters of all kinds (cabin air filter, air filter, oil filter [with oil change]...) are a definite, but there may be extraneous or rather unexpected things that pop up at 100k miles. So I might consider setting aside a little bit of money or however much money you get taken off of the seller's asking price just in case as a small warranty of sorts...
It's already been mentioned, and again, while I can't speak for the SportCombi, I can tell you that Saab's interior construction is rather notorious for squeaking and creaking and rattling. If you're the kind of person who is easily annoyed by those sorts of things, then it may not be the car for you. (I am that kind of a person, actually, but I still went ahead and bought the car. I don't regret it, but I find myself irked by the shoddiness of the interior's cheap plastic trim pieces and peeling radio buttons and such from time to time. Like, "Really, Saab? You couldn't have gone with some heavier plastic, or etched/printed the numbers onto the radio buttons themselves??")
Other than that, you'll save a ton of money by doing your own work whenever and wherever possible. It sounds silly, but just something as minor as having the spark plugs changed would be a $150 job if I were to take it into the garage. (The plugs were $9. I did it myself.) Valve cover gasket? Never got a quote but I overheard another guy get a quote for it... $500. (The gasket set was $21. I'll be doing it myself...)
tl;dr 1.) Do the work yourself whenever and wherever you can to save money. 2.) Find a good garage that does good work and take your car there for the things you cannot do yourself. 3.) Set aside some money just in case. 4.) Don't buy the car if a peeling radio button or a rattling door panel will freak you out. Lol