How can I get started riding without spending a fortune (too much)? I've just recently moved to a city (Seattle) where owning a car seems less appropriate than it has to me in the past.  Before, I lived in a far more suburban environment where biking was more-or-less just meant for trails and your "typical" bicycle was a $150-$200 one at the nearest Walmart or Target.  I'm apprehensive about dropping $500 (or more) on a bicycle currently, and I am really just looking for the best way to get started.  

Do I really just need to drop $500+ on a new bicycle and deal with the elevated costs?  And if so, how do I even know where to begin on what type of bicycle to pick out, since it would more than likely be my primary mode of transportation?
Yeah, buy a used bike somewhere, either at a shop that has a bunch, or off or Craig's List or another "want ad" source.  And, of course, there are yard sales.  If you shop carefully you can probably pick up a serviceable bike for $50-100.

But first study bikes a little to learn to recognize quality.  Look at the cheap bikes at Walmart and some moderately priced ones at a reputable bike shop.  In particular note the differences you'll see around the rear axle and around the crank.  The cheapest bikes will have a 1-piece solid crank, whereas good bikes have a 3-piece crank.  On cheaper bikes the "dropouts" that the rear axle fits into are made of stamped sheet metal, whereas on better quality bikes the dropouts are die-cast or forged.  Also observe the joining of the tubing of the frame -- better quality bikes will have smoother welds, etc.

Also learn how to check out the condition of a used bike.  A little rust is not a problem, but if you pick up one end of the bike and spin the wheel it should spin freely, and the wheel should not wobble noticeably as it spins.  A brief test ride should find the brakes working well and the shifters at least working (they will likely need a "tune up").  Standing over the bike squeeze the front brake and the move the bike forwards and backwards -- the head bearing should not have any noticeable play.  Grab the crank and shake -- again there should be no noticeable play.