I wouldn't spend more than 8k for sure on it.
KBB.com prices the car at around $8k.
I bought my 97 4 years ago and paid $9k for it, however I probably would of paid less if I had known anything about Porsche's and had a Porsche mechanic go over the car beforehand.
Everyone has posted this, but they are right in saying to not trust the dealership and to get a Porsche mechanic not affiliated with the dealer to go over the car.
I also live in michigan, and while 93 octane is the predominant premium fuel, I have been able to find a good number of gas stations in my area that sell 94.
Good luck though
And I hope you realize the costs associated with owning a Porsche haha.