I have won three (over the years) International CO-4070A's for $25.00 (buy it now, these were three different occasions) on eBay.
I got a sealed 1/32 International Eagle cabover at the Toledo NNL for $30.00,
lastly, when I worked at a department store (going out of business), they gave me 125 pounds of .020 styrene sheets (the dividers in the record racks, yes, THAT long ago) for $10.00. I still have about 120 pounds left.
Oh yes, I got a 1970 JoHan Roadrunner for $27.00 on eBay. (blurry picture, sold as a GTX. I took a chance, and the model was perfect!)
I have never found any deals at flea markets or yard sales. I still look, though.