For 4 miles…… one of those OFO bikes off ebay for about £90. It will still be going in 10 years time and will never get a puncture as the tyres are solid!
Only fault with mine is the rear light. Budget for a pannier rack, panniers, and dynamo rear light to replace the woeful solar thing. If you really want to spend your c2w budget get a usb charger etc etc plug into the dynamo.
Only nice to have would be a smaller chainring/bigger sprocket, the 3rd gear is all but useless, and 1 wont get you up steep hills.
I love mine, its a heavy brute of a thing, and not particulalry comfy, but ive left it in town on a saturday night unlocked and its not been nicked!