There are other classified ad services. Find out what is being used "locally".
Craigslist, Kijiji, Letgo, Facebook, Offerup, NickleAds, E-Bay (local if large awkward cheap stuff), etc.
THRIFT STORES.
Many of the people here on the board do our own maintenance, so for a Hybrid, perhaps $50 to $100 USD, plus a bit of elbow grease. Digging the bottom of the barrel, expect to spend at least $100 in tires & parts, but you could well end up with a bike as good as those $500+ bikes, with things like better tires than the stock tires. Not necessarily shiny, but a good solid bike for a commuter.
You can, of course, upgrade tires, seat, etc on your $500 Trek, but soon you'll be in $700.
This Jamis Coda came to me for $50 (thrift store purchase).
I don't ride "flats", and it has a fair number of upgrades, but it suits me better than a stock $500 bike.
