The standard machines called Whimsical, Majestic and Gnarly are permanent, so you will always find them available. The gem cost of each machine will depend on the rarity of the cards it contains. The rarity of each card will be represented by its type: Common, Aqua, Gold or Black.
Each machine will contain an assortment of cards with different rarities. You can check the number of cards of each type by pressing the "?" symbol at the top of the machine.
At the bottom of the machines you will be able to see the amount and cost of the cards it contains. These will allow you to complete the standard series.