I feel like the cheap plastic ones work particularly well for younger kids. A grown up may need to help set it up but they can take a little accidental nudging without getting out of alignment. Look for transparent plastic because it's more fun to be able to see the marbles the whole time. You should be able to find something for $20 at Target or someplace. <a href="http://www.thetoyhunt.com/qa6546.html?productid=qa6546&channelid=AMAZO" target="_blank">http://www.thetoyhunt.com/qa6546.htm...hannelid=AMAZO</a><br><br>
We had a Plan Toys wood one but it needed constant adjustment to stay aligned or the marbles wouldn't roll right. Even the force of the marbles or the vibrations of people walking would mess it up.