Another source many people ignore is native cut gems for recutting. I often buy handsful of native cut garnets at the Tucson shows for just a few dollars.
I just bought a Swiss blue topaz on eBay this last week. The cutting is poor, the polish is worse, but it is 29 x 17mm, and weighs a little over 41 carats. VVSI, and plans are to recut to a smaller and more standard size. The price? $33 delivered.
You will have a hard time finding a piece of rough big enough to cut this stone at this price. BONUS: it’s already preformed!