Are you in the USA? Craigslist & E-Bay are your best bests. Canada seems to lean towards
Kijiji: Free Classifieds in Canada. Find a job, buy a car, find a house or apartment, furniture, appliances and more!
I agree that bike looks cheap from the photo, but most department store bikes had stem shifters.
That bike has downtube shifters which could indicate something better than it looks. Try to get better photos and a make and model from the seller