Yeah its extra work for sure. You dont need front brakes, so that helps. But you do need to fenangle something to shift gears as well as use an axle with a reinforced inboard section for the drive sprocket.
They are a hoot though, light and nimble compared to 125’s so they handle real nice. It’s like having TAG lightness with (most of) the punch of a shifter.
On the higher output, but lower cost side I can’t really think of anything. They are eother cheap to buy and expensive to run (100cc eg FA motors) or expensive to buy and cheap to run (Biland\SA250 four stroke)