I'm buying random cards with gems, and this is the price. You can add bot here to trade in chat.
https://gtm.you1.cn/profiles/76561199631273058/
Currently, prices are:

- Regular Cards
• 1 Regular Card (sets of 5): Marketable: 125 Gems | Non-Marketable: 125 Gems
• 1 Regular Card (sets of 6): Marketable: 104 Gems | Non-Marketable: 104 Gems
• 1 Regular Card (sets of 7): Marketable: 89 Gems | Non-Marketable: 89 Gems
• 1 Regular Card (sets of 8): Marketable: 78 Gems | Non-Marketable: 78 Gems
• 1 Regular Card (sets of 9): Marketable: 69 Gems | Non-Marketable: 69 Gems
• 1 Regular Card (sets of 10): Marketable: 62 Gems | Non-Marketable: 62 Gems
• 1 Regular Card (sets of 11): Marketable: 56 Gems | Non-Marketable: 56 Gems
• 1 Regular Card (sets of 12): Marketable: 52 Gems | Non-Marketable: 52 Gems
• 1 Regular Card (sets of 13): Marketable: 48 Gems | Non-Marketable: 48 Gems
• 1 Regular Card (sets of 14): Marketable: 44 Gems | Non-Marketable: 44 Gems
• 1 Regular Card (sets of 15): Marketable: 41 Gems | Non-Marketable: 41 Gems