I personally will not buy used bikes on craigslist or any bikes online just because you're new to cycling. On Craiglist, everyone knows there's a chance that you may not like the bike after riding for awhile. People who had success in buying from Craiglist are people who knows what they're buying (components, comfort, and most importantly, fitting themselves on the bike). Buying from online retailers is also risky for new cyclists because no one is there to inform you about each bike (new or used) and some models / brands you may see might not be at your LBS to test ride. If you want you save money, I suggest buying used from a LBS. At least, you'll make a more informative purchase and get a basic fitting to make your ride a little more comfortable. Your LBS may also give you a short store warranty with the purchase. I suggest to go to several LBS and compare prices. If you have doubts about how much a bike should cost, get the complete specs of the bikes (usually you can easily get them online) you're interesting in and come back to this forum and ask.