I run three on my line. They work well. I would have more, but as you indicated the price is high. Something to consider. They are great water traps, but they are also very effective for use in land sets. Opossum and racoon will enter them. Comstock also says they will work for bobcats, but so far I haven't tried them on cat sets. I would recommend starting out with one until the price of beaver belts goes up. When you can get a quicker return on your investment then buy more.
Hank