I looked at garage sales, thrift stores and flea markets for bikes for a month or so, and finally bought a "new" bike on eBay. It was assembled for me by the seller (retired LBS owner), and cost me $70 for an older vintage 10 speed (my guess is 1980's) that had never been out of the box. Univega Custom Ten.

In all of my other shopping I had only seen kids bikes.

My first bike (about 30 years ago) was based on a free bike from a friend. I did lots of work, but spent very little money on it. I foolishly laced my own back wheel to upgrade from single speed to three speed, but lucked out on having the proper size spokes.