Caroline,
This question has come up from time to time and to my surprise never really sparked much debate. But, as a fellow noob (newbie) here's my take.
1. I never have really quite understood all of the bike snobbery that is so rampant. I would think that most cycleists would be glad that there is "one less car" and someone is joining the ranks.
2. I have looked and looked on Craig's List without ANY Luck. All I have seen are bikes that flippers are listing, they are marginal bikes and listed at what I consider ridicuolus prices.
3. Not everyone cares to, or should drop by the LBS and plunk down $500.00 or mor eon a entry level bike.
4. Buying used might sound like an alternative, but then you end up buying something that needs alot of attention and the noob becomes disillusioned and quits.
Now, here's what I did. I bought my commuter from Target. But; I did ALOT of reading and research into what went into box store bikes and what went into LBS bikes.
The way that I shopped, I compared frames and components and decided not on the top of the line. But the best that I could afford.
You'll notice that alot of folks are eager to spend someone elses money!!
I read all I could get my hands on for the type of bike I was looking. Also, I read ALOT on as many bike parts store such as Nashbar, Jenson USA, Price Point and Performance Cycle. You'll quickly get a feel for what is top of the line, what is mid grade and what to avoid.
So, for $200.00 I got a Forge from Target (Forge framesets are made by Giant). It has Shimano drive train, Tourney RD, Shimano FD, Suntour crank , Kalloy adjustable stem, Pro MAx V Brakes, Kenda Tires, Shimano Mega Range gearset, Suntour Front Fork, Kalloy suspended seat post, Quando 36 spoke Hubs front and rear with 14 guage stainless spokes.
Is it the best? No, I have just over 500 TROUBLE FREE miles on it. I ride it to and from work. I have added some other items to it and feel that I have just as good of a bike as anyone. SO, do your due diligence, shop wisely and buy the best that YOU can afford and then enjoy yourself.