Instead of blowing your budget and your back, make a hypertufa trough like this one.
Forms are often made from wood, but this 1-inch-thick foam insulation board is easy to find and you can cut it with a craft knife. Measure the size you want. Here, the pieces were cut to form a 16-inch square about 8 inches tall. Scoring the foam is an easy way to get a clean, straight edge. Simply run the craft knife along the edge of a ruler, then set the foam on the edge of a table and push down to break it.