If it passes all the mechanical tests (which must be conducted by an independant mechanic) and comes with all receipts and detailed, accurate service records, you're on to a good start. Also, the mileage in my opinion is not particularly scary, you would have to expect that a car approaching 10 years of age (or is 10 year old) will have anywhere between 100,000 to 150,000 klicks on the clock. You have to consider that the average car does about 10-15,000 klicks a year, so mileage on this car does not strike me as excessive. Also just out of interest, find out if it's mainly highway klicks or city klicks; an interesting way to determine clutch wear if it's still original (on the slight chance).
As for market value, I think a price anywhere between $20-25k is a fair price, but I could be wrong; other guys here will give you better advice than I can on this and other more detailed mechanical issues.