The Gyarados ex (109 / 112) card can be found in the Firered and Leafgreen set.
Recently sold 4 times and based on those sales is worth around £64.36.
Currently, there are 4 open listings for this card on ebay.
This card sells in the range of £44.54 to £84.18, making it quite volatile.
This Rare Holo Ex card was illustrated by Hikaru Koike.
The fact that it is a EX card makes it one of the more valuable cards.