I have a 10, 8 and 5 year old that want to get out this year for first runs. We have a good stock of larger (130+) boards, but nothing smaller for the little guys. Preference is to keep it cheap because it will probably only last 1-3 years until they outgrow it.
Found a cheap board/binding combo at Walmart (Nash Jr Wakeboard) for $94. http://www.walmart.com/ip/Nash-Jr.-Wakeboard/8812067