welcome to the forums...lots of good used bikes available on craigslist, depending on your area... if you are a total newb as you stated, maybe take one of your experienced friends along to help you check out the bikes and check on fit...
there are lots of good bike brands..I have 4 bikes at the moment, 4 different brands...i go by how the bike feels, and how it rides, not the decal on the frame.