Craigslist is excellent! eBay is very good and it will allow you to understand what the market looks like for used bikes.
Here is a website for a dealership a friend owns in Dallas. You can use it to compare prices as well.
As a new rider, I’d shy away from a brand new bike regardless. Too many variables starting out. FWIW…I’ve only bought one brand new bike…and I don’t think I’ll ever do it again!