I would second learning basic maintenance and a cheap old bike is great place to start. A lot of the items on my list are "risk factors" for lack of a better word. If you want to buy a bike with steel rims just to ride around on in fair weather that's fine. I think it's dangerous to commute on one if rain is a possibility.

Stem shifters are something you might get on an otherwise decent bike. The question for me becomes how many compromises am I willing to make on an old bike before something like a Denali from Walmart starts to make more sense. At least you know who your dealing with and if something breaks in the first few months you have some recourse.

For example, there's $150 Schwinn Super Sport on my local craigslist. The tires look like they're shot, and it's got pretty crappy components. Granted, the frame will last forever, and aside from a few scratches, it would probably clean up OK. But I can't really recommend that over a Denali for somebody whose just looking for a bike to ride. Now if it's somebody who's really into old Schwinns or or likes fixing up old bikes, that's a different matter. This is not really an endorsement of a Denali, it's really a matter of what's the lesser of two evils.

My guess is that if the seller has much sense for the market, you could talk them down to under $100. But it's going to cost you at least another fifty carefully spent dollars to make this a reliable bike.

In this market, if somebody has at least $200 to spend, they're starting to get into the realm of reasonably modern quality road bikes that are ready to ride.