I am in need of a trail-a-bike for a 4 year-old who is just about to learn how to ride on his own. A trail-a-bike is one of those contraptions that attaches to the back of a regular bike and creates a tandem situation for kids to help learn to peddle and ballance. He just needs a little more help, so I only want to pay about $50 to get him over the hump. If you have a trail-a-bike that your own children have outgrown, it would be of much use to us. Thanks.