To find out your specific used car value, you'll need to investigate using something like the Parkers Guide ~ this is a publication available at most good bookshops which shows guideline values for all most used car values. The guide is issued yearly, so try not to refer to one from a few years ago which won't be as accurate! If you are thinking about selling your car, you should also check out listings for similar makes as yours ~ in terms of model, age, mileage, condition and Tax/MOT validation. Once you have done your research, you might find that your vehicle is actually not worth as much as you originally imagined. In this case you might already have a new car in mind ~ perhaps consider supplementing your sold car value with some car financing which could help you get a newer and more modern vehicle.
You can also try www.kbb.com or www.edmunds.com. They price your vehicle based on mileage, your opinion of its condition, and so on.