Which Gyarados ex do you have?
Same name, 75× the price: $1.87 to $140 raw. The difference is printed on the card — it is just not somewhere most people think to look.
Fire Red Leaf Green · #109
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$140
9.9% gem
BREAKpoint · #26
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$18
9.5% gem
XY Black Star Promos · #XY106
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$14
22% gem
Scarlet ex · #091
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$12
91% gem
Scarlet & Violet Base · #225
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$11
43% gem
Scarlet & Violet Base · #045
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$2.92
43% gem
Scarlet ex · #014
Check the set symbol in the lower right of the illustration, and the copyright year along the bottom edge. Those two identify the print run on every card that has them.
$1.87
87% gem
We have no hand-checked note for these printings yet, so the guidance above is the general rule rather than something specific to this card.
Prices are raw market value. Click a printing for its full grading verdict — the gem rate, the fees and whether it beats selling raw.