Couple f355 things from my experience:

1. Get one that has documented proof of maintenance performed
2. Get one that has new valve-guides that are not bronze
3. Get one that has aftermarket high-flow cats, and has since had the headers replaced
4. Try to find one with a challenge grill, if not, plan on putting one on ASAP, it's not just for looks
5. Make absolutely sure the top is functional if its a spyder
6. Avoid F1 models, the pumps are weak and the clutches wear out fast, they are cheaper though

If nothing major has been done, plan to spend the following:

Valve guides: 7k
Headers: 7k
Major service: 5k
Grill: 2.5k
Cats: 2.5k
2 cans b44k: $30

 

I love the 355s, but the 360s have come down quite a bit in price. Get one with more than 20k miles and you'll see a significant price drop. Might be worth considering...and we make a TT kit for the 360.