Another kind is the Mauisails Race Light strap. I use these as the chicken straps on my formula board and they work well. Probably nowhere near as comfortable as the Kowalski straps (apparently, i haven't used them) but if you're not using them often (ie on a SUP or as Formula chicken straps) then might work for you? $70 for a set of 4.
I tried the Dakine Slims before on my board and found that while they were lightweight, they were horrible in the comfort section! The Kolvaskis are supposed to last 3x as long as normal straps so I believe that is why they cost that much. I haven't personally tried them on the water yet but my sponsor (dealer) has em in stock and wow they were pretty light when I picked them up. They also seem to have more support than the Dakine slims.