My Grand Am is dead

Well, my Pontiac Grand Am GT 1999 died this weekend. I changed the oil and was checking all the fluids and discovered something quite unpleasent when I got to the radiator fluid. Much of the interior walls were coated in a dark green, thick fluid. The fluid itself wasnt as discolored as the walls though it was clearly not bright green. I had the vehicle checked out and the mechanic said that the cars intake manifold gasket was going and that the head gasket was also possibly going. The estimate for repairs was $1,700 and a new engine would have cost 3,500 including labor. The total price of the car from KBB was around 4,300 so I am going to either trade it in to a dealership or donate it to the Bart Star foundation (program to help troubled youths). I am now in the market for a new car. I am looking for a reliable, fun, practicle car with a price range around $20,000 U.S. The worst thing is that the car only had 108,000 miles and everything else in the car is in great shape considering. I am looking towards sedans and some of the larger hatchbacks, your suggestions will help.