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I am interested in buying a folding bike, I think the biggest issue for me would be weight and price.
The most I'm willing to spend is $200, maybe $250."
Keep a look on the Best of Craigslist thread here, folderisti get upgrade-itus every three months, and there are often quite a few bargains. Maybe a folder with 16" wheels will be light enough for you, there's plenty of choice. They weigh around 11-12 Kg, whatever that is in foot-candles. New, the Downtube Mini is making a lot of people happy on here, if you can stretch to one. Have a look in the bike shops if you can, at different models. Folders can be rare in bike shops though.
Gears are good, rear racks carry books and sandwiches, saddles can be changed to suit. Bikes do wear, so you'll need a small budget for repairs and punctures.
Light weight is better, but costs real money, for very little weight reduction. Just get fit in the first month or so and take it easy. 11-12Kg is no problem.
If you stick around here, the members often point people towards good used bikes , especially if you stay communicating and update your sig to show your approximate location.
Bon Chance!