We bought something similar at canadian tire for about $30 if I remember correctly.. not as high quality as the originals, but our son's been on it since last year and its still in good shape... both this one and the one suggested by the previous poster are 10" versions though which are slightly shorter than the originals (12"). Its just at the edge of ridable but he's almost ready to move on anyway.
Here is is:
http://http://www.canadiantire.ca/AS....jsp?locale=en