[Highland Park] G scale train?

Hi, My 4 year old (who is obsessed with trains) was given a used G scale Bachmann circus engine and a lot of track. He doesn't have any cars for it though, and I'm looking for some train cars. Any train buffs out there interested in parting with some train cars? Don't care how used they are - this lonely engine just needs to pull something around the track! My son would be happy with anything. Looking for something pretty cheap. Cheers, Jill