79letour - Sign on to Mysubaru.com and see what the GTP (Guaranteed Trade in Program) value of your car is (you will need the VIN). It may be higher than you think. Mine is about $20k.
Dealer has to give that to you if you trade in regardless of the price of the new car (I normally pay Invoice or a couple of bucks less).
Edit: As long as the car has not been in an accident or has body damage, etc.. See the GTP rules for the specifics. Don't believe that the trade has to be accomplished at the same place you originally purchased your car - Any Subaru Dealership.