To negotiate the deal, whack the owner on the brake pedal, safety, et al and knock the price way down. To analyze the pedal symptom, consider the following:

-air in the system, fixed by a power fluid flush ($50)

-soft brake line in system (not likely but it has happened): fix with new line ($100)

-leaking seal in caliper (check all four calipers for leaking brake fluid); again not likely but it has happened: fix with rebuilt caliper ($150)

-faulty master cylinder seal; fix with rebuilt master cylinder ($300)

-other problems such as seized caliper, proportioning valve, etc. all not likely and easy to fix.

My STRONG suspicion is that the problem is the first (air in system) and you will fix that with the power flush that you would do anyway because this car will need new brake fluid at least every two years. In a humid climate such as Florida's I would consider doing it every year.