As an example of what you can get in the used-bike market, I picked up my 1983 Nishiki Cresta for $275 and use it for my 6-mile round trip commute everyday. Good solid bike, but I have needed to replace several parts along the way. The stock seat is terrible and toe clips are tiny. The Suntour derailleur will "complain" when shifting to several gears, but is solid for the most part. Handlebars are a bit narrow for my frame, 6'0 180 lbs.

However as a hauler, the thing is a beast. No braze-ons for a front rack but I can easily carry a change of clothes, lunch, a laptop, patch kit + spare tube + spare tire levers + a heavy lock. If money is an issue and you end up on craigslist, I'd recommend checking it out!