Welcome to the site!
The used Grand Prix market has been stable to slightly increasing lately.
One thing I would do is check out www.kbb.com for a price in your area. The car itself, if properly maintained, will last a long time. Figure 300,000 miles plus. Recently in my area there have been a couple "SE" cars for sale in th $4500 range but they have more miles on them (150,000) and may not be quite as sharp as this is Michigan and Michigan winters feature LOTS of salt on the roads.
And of course, no one ever pays the asking price
