The Nexus 3-speed is probably the cheapest option and not a bad choice if you can route the cable through the frame. The twist shift can be matched up with Nexus-specific grips (Ergon etc.) to make it blend in more. There's nothing much on the shifter to catch and break anyway I reckon. 80% of riding in 'high' gear, middle for starts and hills, low as as a rarely used granny gear is my pattern. So not much thinking about shifting, or even shifting full stop.