I found a small airplane table lamp with its original shade in a junk store for $6. At the time it would have been worth about $100. I expect it's worth a bit more now.
I once found a re-covered* table in a dumpster. I'm guessing the owner thought it was unattractive and replaced it with something from IKEA. "As is" it would retail for about $600-$800 in an antique store. I kept it and it's in my living room.
* a re-covered table is a table from the 18th century that was brought to America from Europe. The original top would have be salvaged for the wood and a pine drop-leaf top put on the original base. The base can be several hundred years old while the top will be about 100 years old.
My best would be a 15th century woodblock print from Dresden, Germany. The second best would be an 19th century Inuit Carved Bowl. I have had neither appraised and I don't think I will. Oh...I paid $1 for the print and $5 for the carved bowl. I love to antique and flea market.
My best ever bargain was a bar height bistro table with chairs. The table has a gold filigree design, with a second filigree design carved into the wood. The table top is on wrought iron pedestal legs. The chairs are a mahogony leather. I absolutely love this set!! My cost $200.00...value $2000.00.
I actually knew the person, and he gave me a serious deal, that he would not have given to any other.