If you google [yourcity] yard sales, you'll probably come up with a site for that city and for surrounding towns (for example "Houston yard sales". These are listings like newspaper classifieds -- people wanting to buy, sell or give away items, not listings for yard sales. Then just search for sewing machines. I check the ones close to us periodically, and there are always sewing machines, both with and without cabinets that people are practically giving away. In fact, I bought a 1-yr. old king sized Serta pillow top mattress for $100 from one listing.
Good luck.