Most people don't go per card, but per 100 cards, which would be, in most cases, 1 coupon.
The easier it is to hunt, the lower the price, like Hydra cards at 3k for 10 coupons.
The less the mobs the harder to hunt, the more expensive they get like 100:2 for Carat cards and maybe Matyr cards, and Metaller cards, depends really.
Take time to learn what card would cost what (as well as looking through the Forsaken Elite Set guides), with the exception of Hydra cards, there are cards priced at 100:1, 200:3, 200:1, and so on.