I'm not sure anybody has ever tried to sell the backplate concept as being the cheapest way to rig yourself for scuba. I'm certain that many of us have commented that it is not the most expensive, however. And as already pointed out above, in the LONG run, a backplate and wing will be cheaper, simply because you don't have to replace it all if one component fails.
But when you compare prices, you have to compare total functionality. If you buy a weight integrated BC, you have a place to put your weights. For a BP/W, you need a weight belt, or weight pockets; that's an extra cost. A BC may have storage for small items, but a BP/W requires pocket shorts or pockets on your exposure protection, which may be an extra cost, depending on what exposure protection you are using (as many dry suits come with one or more pockets). In the end, it's unlikely you are going to conclude that a BP/W is the cheapest option out there, even if you go bottom-shopping for the components.
But I don't know about anybody else, but when I participate in an activity I do for fun, I want to be comfortable, and I want the equipment I use to work as intended and as I envisioned when I bought it. I don't want to fuss with something, and I don't want to buy something and then find I'm having to compensate for poor design. I like my backplate and wing setups because they are adjusted to fit me, so they fit me every day. They put my ballast where it belongs. Dual cambands make for better tank security. The whole thing disassembles for packing and travel, and reassembles in minutes. All the components except the wing itself are easily sourced, serviced, or replaced by ME. It's efficient and it works, and it didn't cost any MORE than doing something else. That's plenty good enough.
But when you compare prices, you have to compare total functionality. If you buy a weight integrated BC, you have a place to put your weights. For a BP/W, you need a weight belt, or weight pockets; that's an extra cost. A BC may have storage for small items, but a BP/W requires pocket shorts or pockets on your exposure protection, which may be an extra cost, depending on what exposure protection you are using (as many dry suits come with one or more pockets). In the end, it's unlikely you are going to conclude that a BP/W is the cheapest option out there, even if you go bottom-shopping for the components.
But I don't know about anybody else, but when I participate in an activity I do for fun, I want to be comfortable, and I want the equipment I use to work as intended and as I envisioned when I bought it. I don't want to fuss with something, and I don't want to buy something and then find I'm having to compensate for poor design. I like my backplate and wing setups because they are adjusted to fit me, so they fit me every day. They put my ballast where it belongs. Dual cambands make for better tank security. The whole thing disassembles for packing and travel, and reassembles in minutes. All the components except the wing itself are easily sourced, serviced, or replaced by ME. It's efficient and it works, and it didn't cost any MORE than doing something else. That's plenty good enough.