I have a couple of candidates.

The proa (it has 2 hulls) that two guys had built out of aluminum ducting from a description on the internet. They tried to sail it but, the main hull just folded up and it sank. They were going to leave it, but the Deputy that patrols the park had a talk with them and they hauled it away.

The cheap inflatable catamaran (vinyl round hulls, no centerboard, flat plywood rudders) I heard that one of the local discount places was selling them for $99. I saw 4 or 5 of them in the late 80's. In no case did the sail go well.

The tunnel hull Moth. Think 75 lb Hobie Bravo with a good sail rig. The Class Association outlawed all forms of multihulls. If they hadn't outlawed them, we would have a real 12 ft sailing class now.

My vote would go to the Moth Class Association as lower than the cheap inflatable.