I thought you all would get a kick out of it! We'll see how broke he is when Seth gets home on Tuesday, so far he's been a dream, almost like he's just a toy.
We paid 60 bucks for ours, I added the bridle and reins. I also added more hair to the mane, and I'm thinking about adding a saddle too, but I have to think of something that is weather durable. The seat could be a little uncomfortable because it's sunk down with high sides, so I'll have to find something.
For those who want to make their own: http://davesgarden.com/files/Pony_Tire_Swing/