On average, you can find a single gold Pokmon card in every two boxes that you open
You only need to cast a few instants or sorceries before Rite of the Dragoncaller pulls its weight
Yet the only for sure way to get rare cards is by opening a lot of packs, either twice daily with the games free mode and more beyond by spending hourglasses, or with an additional daily pack with the games paid premium mode
Most often it is a promo card (look for a black star and the word PROMO), a Japanese card (which uses letter codes instead of shapes), or an older or non-standard print
Collectors also appreciate the Japanese print quality, which is considered top-tier
$50 is already fairly expensive, but $100 is a predatory price point for whats included in these precons