The Moltres ex (31 / 40) card can be found in the Nintendo Black Star Promos set.
Recently sold 5 times and based on those sales is worth around £21.00.
Currently, there are 4 open listings for this card on ebay.
This card sells in the range of £13.58 to £28.42, making it quite stable.
This Promo card was illustrated by Ken Ikuji.
The fact that it is a EX card makes it one of the more valuable cards.