I have used a common freewheel hub, (not flipflop)
moved , equalizing, right side spacer width, to the left side of the hub axle.
to center the hub on the axle , de dished the spoke tensions
and my cost was just the single cog freewheel.
( Here, not flat, and I , no longer young , I've re adopted IGH for at least 3 speeds )
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