yeah it's pretty sad. Most of them are worth not much more than the paper they are printed on. I buy/sell my cards at https://www.cardmarket.com/en/Magic, you can easily check the prices. Shivan Dragon from 4th edition is around 0,19€ in excellent condition. Phyrexian Dreadnaught though still sees some play in certain decks and is worth around 12€ in a good condition. Hammer of Bogadan is practically worthless (0,02 €). (Crimson Hellkite 0,12€)