How much are Yu-Gi-Oh cards worth?
Depending on the effect, the value of the card depends on how strong the card is in the meta-game.
for example, a 5 star monster like:
Vortex The Whirlwind: is less than 3 dollars.
however, in the same set, a 1 star monster like:
Maxx "C": rises to around 30-40 dollars.
so, in reality, it depends on value, and the current effect on the meta-game. also, rarity plays role in value as well.
Well that depends on the card, each cards value is based on rarity. Here they are (from cheapest to most expensive)
If you need a key to identify these, Google something like yugioh rarity guide. Then you have a guide of which cards are worth more than others. If you need specific values, then look on eBay for a rough guide.