The official bulk card pack optionFirstly you can use the bulk buy option on the Steem Monsters website, which will give you 10 free bonus packs if you buy 100 packs at the same time ($1.82 per pack, 110 packs in total), or 75 free bonus packs if you buy 500 packs ($1.74 per pack, 575 packs in total).
SmartsteemAnother option for getting cheaper card packs is to use Smartsteem. This website is a certified vendor of Steem Monsters card packs, and it does provide a loyalty reward program. This loyalty reward program will make it gradually cheaper to buy more card packs.
Total Packs Purchased
0: 1% Loyalty Reward - $1.98 per pack
200: 2% Loyalty Reward - $1.96 per pack
1,000: 3% Loyalty Reward - $1.94 per pack
2,500: 4% Loyalty Reward - $1.92 per pack
5,000: 5% Loyalty Reward - $1.90 per pack
With the maximum bonus of 5 % loyalty reward, each card pack will cost you $1.9. However, it seems very unlikely that regular players will ever be able to get to this point, since it seems highly unlikely that regular people buy at least 5,000 card packs.
The good thing about Smartsteem is that they don't require you to buy them all at the same time to get the discount, in contrast to the official bulk buy option. This makes it a much better choice for everyone who enjoys buying a few card packs daily or every once in a while, instead of the whales who buy hundreds or even thousands at the same time.