A good price for any Lexus is going to be around 5 to 8 thousand dollars for that year and also depending on the condition and mileage. It could be more or less depending on those factors plus if there is any damage and any work that it may need.
You need to check the blue book value of the vehicle for that condition and the year of the vehicle. Their really isn't alot of ways to really find a way that would give you the correct prices. Because different cars go for different amounts depending on the history of the vehicle.
If you need to know the price of a used car you should check he vehicle pricing guide. Kelley's Blue Book and the N.A.D.A. Guide both allow you to look prices up online. Just put in the cars information and it will give you the values.