I have found a sprite bottle works quite well. I could probably get 3-4 more horsepower out of a moutain dew bottle. I'm working on that mod.
Milk jugs do not work. They ingest water.
Believe it or not... that set up I have is super dry and my engine compartment is always full of water.
You could make one out of glass. The key to a good airbox is channeling the intake to the top of the head or the center of the ski infront of the engine. It stays dry in the center because the water rolls arround the edges. K&N and the others work great when the ski stays upright like during races. When it's sloppy and you're rolling, get w/e box protects the hull side of the carb and gets the air from the center. That's why mine works so well even though it's ghetto. It protects the wet side and pulls from the dry side.
Anyway... K&N sucks. The stock Yami box looks like a good set up. I'd go with that.