Besides the Basic Fairy Energy card, these cards have mostly maintained stable prices since release and cost in the range of $4-20
I personally run Spawnsire of UlamogSpawnsire of Ulamog in my Kruphix, God of HorizonsKruphix, God of Horizons deck, but only because I've run it by my group and they've all agreed that it's hilarious to dump a bunch of random Eldrazi onto the battlefield
If nothing else, hell stop your vampires being chump blocked
In other words, that's four mana of value you can gain the same turn she enters the battlefield
This means Druddigon can escape for free, as can Hitmonlee and Marshadow, while Graveler and Golem can retreat for a single Energy
Now that you understand the board and zones, you're ready for the next step: learning how turns actually work