This can be tricky, as the value of cards can vary greatly depending on some factors, as discussed earlier
So if there was ever anything worth some real cash the seller came across, no way is it knowingly being wrapped back up and sold for $8 with 49 more cards
Pokemon Center exclusives (like Prismatic Evolutions special collections) often drop without warning
This includes pieces of text that may not be explicitly about the card theyre on but are still great complements
A lot of balance and care goes into choosing the cost of a card, more than I can express here, but looking for similar effects on existing Magic cards can give you an idea of a fair costfor example, a ramp spell that puts two lands into play ought to cost 4 mana, per Explosive Vegetation
It could be to pay for a different cards cost like Abandon Hope , because a spell requires you to, or to reduce your hand back to its maximum hand size