About $25 to $30 for a 4' by 8' sheet of FRP (fiber reiinforced paneling) Roll them in a tube long wise and over lap the ends about 4" for glut ing. They sells a FRP adhesive that cleans up with water or you can use contact cement. That will give you a 14 inch diameter tube 8 foot long. What works well is to make a simple plywood trough that is 24 inches wide inside and 18.5 inches tall inside. Make it about 6 inches shorter than your tubes. Cut yur tubes to your esired length, roll and glue them. Tape until dry. After drying ush the tubes into the trough. The first tow will go right in without effort. The next two will take a second person usually. To get the third into the trough the first tubes must be deformed into oblongs 8 inches wide and 13.5 inches tall. To get the third tube into place all the tubes must be squeezed sideways until the tubes are 6 inches wide and 18.5 inches tall. There must be cross pieces across the trough to hold the tubes down and maintain the oval shao pe and to keep the trough top from spreading. One on each end and one every two feet approx.
For SOG grows budded straight from rooted clones it is possible with intermittent spray to go a full grow with nearly no roots laying in the tube bottoms. For ends just use plywood ovals covered with some of the extra FRP paneling. The paneling is only about O.10 inches thick so it must be supported in a trough. Sure beats root rot and pythium problems and allows for a much larger roots sytem than small tubes, posts or gutters. The ends would just be a 12.5inch by 6 inch rectangle with a 6 inch diameter half circle on each end. Cut the bottom 1 inch off the plugs on the drain end and simply drain to a short piece of gutter with a down spout. The plugs can be merely pushed inside the ends of the tubes as friction will hold them in place. Not cheap but neither is large pipe and even large pipe provides much less root lengths. Should run less than $150 total for a 24" wide system up to 6 foot long. Plus the tubes would be deep enough for a high pressure aero or an atomized aero system.