I think what's challenging is the 'cheap/ugly' requirement. One option would be to get a decent yet used cross frame and find a good welder to install some Paragon sliders, which are very high quality. They have a Rohloff specific sliding dropout, and you can mount anything, another IGH, derailleur, singlespeed, fixed, whatever. $300 (used frame) + $100 welding + ~$200 sliders. not too expensive