Highland Park: I'm Looking for a New (Old) Bike

Hello, I'm looking for an old bike that could be a decent commuter if I put some time and effort into fixing it up. I would be especially interested in a steel-framed bike from the 1980s (or so). Road bike or mountain bike. I'm about 5' 6 1/2". I don't care if it's in good condition, though I would like to see it first so I could get a sense of what repairs would be needed. I would be willing to pay in cash or check up to maybe $50 depending on the bike, but would prefer around $20. Thanks so much, Lucy