I found a decent deal on 20-inch sonotube... $69 for a 12-foot section. They're not willing to sell a partial tube, and I don't need anywhere near 12 feet, so I'm hoping to find someone who wants to go in on it with me. Drop me an email if you're interested!! They don't have it in stock right now, but they said it should be in before too long. I cross-posted this to the Austin DIY thread in "local HTF meets".