You have a really nice tractor on your hands. My dad's 1st tractor was a 106 and I have searched high and low to find it. The condition of that 106 is a lot better than what most of us find them in. The hole in the seat is not that big of an issue, the carb rebuild kit is $12 and a new wiring harness is somewhere between $60-$80 (guess)
http://www.ebay.com/itm/Cub-Cadet-72...IAAOxy~g5RvHSr and a new plug wire, maybe $10 or less. So for around $100 you would have a very nice, solid garden tractor. Bet you cannot go to the store and find one for $100, let alone one as solid as that one!! If you and your son worked on it, then it might be something he wished you would have kept years from now......as I wish I was able to locate my dad's 106. Just something to consider!!!
Cub Cadet 123