eyeride

I am building a chain-driven unicycle out of a kid's bike with 20" wheels. The rear coaster-brake wheel will be converted to a fixie, but the front wheel is just leftover. I wonder what it would take to make the front wheel into a replacement wheel for the uni (it has colored spokes & rim which will match it), one with a different gear ratio for example. It looks like new fixie hubs are too expensive, but I could get another coaster hub for $20, then I just need to do whatever it is I'm going to do to the rear wheel to fixie it, and get a new coaster sprocket for <$10. I've never built a wheel, but this might be a good low risk experience. Am I overlooking something? Is there a better way?