Here is a technique to use.
Go to
www.autotrader.com. Do a search on your year and model number in a area of say 100 miles from you.
Select as many cars from this search as you can that are comparable to you car in miles, options. etc. Toss out cars that clearly do not belong in data, ie Porsche dealer cars, odd colors, options that are inappropriate.
What you are looking for is what other private parties are charging for a car similar to your own. with emphasis on miles and color.
Assume that you will realize towards the bottom of that range and you should have an idea.
Out here in SOCAL, you car might bring $20K but it would depend on condition, as it always does.