I believe that bicycles, even pricier ones, are one of the most affordable transportation choices around. However, I can also appreciate the fact that a lot of folks out there find it difficult to fork over a few hundred dollars to purchase a new bicycle. If you are in the market for a bargain, please remember that you are not likely to get one at a large-box retailer. A better choice would be to find a decent second-hand bicycle from a reputable source.
What is a reputable source? That's a hard question, since no one wants to inadvertently end up with a stolen bike. However, there is certainly a lot to be said for re-using existing resources. Here are a few places you may want to try for used bikes:
Working Bikes Cooperative, or another local shop that repurposes donated bikes, usually as part of a youth training program, or other charitable activity.
A local garage sale, where you can be pretty sure the bike being sold belonged to the person selling it.
Online classifieds, but take the time to verify that the seller can document where the bike came from.
Word of mouth, or Facebook community groups, such as Chicago Family Biking Community.
Here is a list of things you might want to think about before purchasing a used bike:
Are you compromising on fit, because it appears to be such a great deal? If the bike needs minor tweaking (saddle replacement, taller handlebars, etc) to make it comfortable, that's one thing, but no amount of tweaking in going to change the size of the frame, so make sure you find something that's appropriate for your proportions.
There may be substantial wear on the hidden bearing assemblies, that may translate into a fairly high repair bill down the line.
Once the bicycle changes hands, original manufacturers warranty no longer applies (this is obviously less relevant if you are buying an older three-speed or cruiser, but could be important if you are buying a newer bike).
A private seller will rarely offer any satisfaction guarantee. Inspect the bike carefully for bends in the fork, cracks in the frame (including on the underside of the frame), and wobbly wheels. Sellers may not have a good understanding of the actual mechanical condition of the bike.
It may take a lot of time and searching to locate the right used bike for you.
After you have paid for any repairs or modifications on the used bike, are you still getting a bargain? For example, even if the bike is in decent riding condition, you may still want:
different (better, smoother, puncture resistant) tires
more comfortable saddle
taller stem, or seatpost, or both
People can and do find great deals on used bikes. I bought a terrific single-speed Chicago Schwinn Breeze several years ago for $30. But make sure you expectations and budget are realistic. Although a typical bike from our store is likely to start at about $500, you may find that, in the long run, it is affordable and fits you and your purpose better.