Hardy Bougle MkIV bought on closeout from Harrissportsmail in UK, $230.
S/N 034
Here, swinging streamers to check for summer rainbow holdovers, but 2 surprise stripers instead on the 5-wt. (ate them, too - hey, they eat our rainbows)
Fished the reel for 5 years and sold for $625 (full disclosure, including the photo above)
This was after Hardy moved production from England to Korea for Mk V, VI, and VII, driving up demand for the 1000 MkIVs out there, and every older Hardy reel that said England.
Made $395 profit in addition to initially saving $395
This isn't the most dollar profit I made on a reel that I also fished - that belongs to a 1917 Hardy St. George I fished 4 years and sold for just above double what I paid - but the 180% profit is noteworthy, making the Bougle purchase an absolute steal - definitely answering our OP's question.
Several other nice benchmade fly reels, Ted Godfrey, Peerless, Kusse Leonard-Mills, I fished and later sold for $200-500 profit, either because the maker doubled their bench prices or stopped making and demand took over. I'm not dumb, if it's burning a hole in my pocket, I sell it.
Speculating and repairing antique reels is another story.
and yes, turned all that into other tackle. A few years later, Hardy USA complained about Harrissportsmail prices, and Alnwick forced them to raise their prices if they wanted to continue selling Hardy.
Hardy has also since moved production of a few reel models back to England from Korea to strengthen their market value.
I haven't played the game in a long time, because it takes up too much time to do it well, but if you want to see what's out there, Lang's Auction is this weekend.