potential canadian buyer wants advice

[the ant]

I came across a '98 Boxster with 140,000km. When I test drove it today, I think that the car is shaking a little bit when the engine is idle (but it seems to drive/rev fine otherwise). Is it normal? Should I be concerned?

The condition is not mint, with some usual wear on seats/carpet and some scrathes/dents here/there that would be expected from an 8-year old car. Owner is asking for ~cdn$20,000 (which is a few thousands dollars less than some typical '97-'99 here in Canada with about 7-80,000km). Is it worth it?

I have another daily driver so it's going to be my 2nd car and likely weekend cruiser only, but I don't want to get a 'money pit' either. How much should I expect to spend on maintaining a relatively high mileage Boxster like this one?

Thanks for help and sorry if similar questions have been asked million times... (Too lazy to search)