Daily driver in a four season climate with north of 100K miles onboard?
My advice, look for a car with much, much less mileage or start clearing out space for all the parts you'll be replacing on the car. The big expense in keeping them on the road is the parts and not really the labor.
If you want to press your luck with a high mileage car, then you need a pretty long list of repairs that have already been done. Namely, suspension, clutch/ims, and cooling components (the big three $$$). You could easily spend very close to the value of the car doing all of these.
I would recommend you download a copy of 101 Boxster Projects for your Porsche Boxster from Google Play or getting a hardcopy. It will cover all the big repairs, the cost of parts and labor. Once you're familiar with this car and find a car you like get a pre purchase inspection done by Porsche dealership. I think I paid less than $200 for top to bottom diagnostic down to which coil packs needed replacing and a very "interesting" looking estimate of all. But I knew what had to be done. Budget to that list of "need to do's" the things that typically fail on a high mileage car that look fine during physical inspection but go without warning like your AOS, starter, alternator, etc. Winters are
very hard on these cars.
http://www.amazon.com/Projects-Porsche-Boxster-Motorbooks-Workshop/dp/0760335540/ref=sr_1_1?ie=UTF8&qid=1415731542&sr=8-1&keywords=101+projects+for+your+porsche+boxster