Most of my good "wild finds" happened back in the late 90's before collecting was even a consideration...I got Snatcher for the Sega CD for $5 at a used CD store...Guardian Heroes for the Saturn for $7. Sealed copies of Rayearth, Shining Wisdom and Shining the Holy Ark for $5-10 each when they were on clearance. No one ever thought they'd be worth dick in 10 years.
My best "collecting era" find was probably a Neo-Geo CD, 2 controllers and 20 games for $150.