Clunker threads in C&V = 'good for ideas'
There is always a mid-range. MTB & ATB bike frames should easily meet your goal - financial and durability. Aluminum mtbs (well inspected for cracks at welds) frames make good commuters - rigid frames, larger tires.
1982 Harding (Holdsworth Special) 531 was $150
'72 Zeus frame + fork, 531 metric, $100 + shipping, with a story. Sometimes the story is the best part.
let me find current pics....
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Vintage, modern, e-road. It is a big cycling universe.