A coin I found at a shop loose in a '10 cent box' full of foreign coins. 1909 Newfoundland One Cent. It was AU looking with a good shine. It's highly likely that this one slipped through the coin shop owner by mistake, it was easily a $75-$80 piece on ebay. I sold it a couple years ago. 1909 One Cent has a mintage of 200,000. I should have kept it as an investment but oh well.
32 walking liberty half dollars, price, $16. Also, $36 face (including walkings) of silver coins for face found cry this year. My best deals for ebay coins is a 1916 d G maybe VG grade walking half for $10, a small z shaped scratch was the thing that helped me get it for so low. Also, two seated halves, 10 bucks each in g-vg, 1876 s and 1855o Coin shop Plus hundreds of 1800's copper (a couple small silvers my coin dealer throw in for me) world coins (mostly Europe and canada)
There are a lot but these come to mind: USSR mint set for 7.50. Sold for 310. I also got two other ones that sold for over 250, bought them together for 4. Got a silver dollar buffalo commem for 25, sold for 150 I think. About 5o silver proof statehood quarters for 70 dollars, sold for 250 I think. A west Germany proof set for 6 dollars sold for over 100.....I got all these and more from mostly flea markets, also from ebay, the occasional show, etc