If you're hoping to improve your character -- and increasing your character is what Diablo IV Gold is all about, you'll require a lot of legendary gems: to find the right ones to suit your style, to earn good star ratings to enhance the gems you have, and eventually to include them in the gem's extra resonance slots. It's endless.
There are a lot of Diablo Immortal's upgrades, currencies, and reward systems, legendary gems are where the business model bites the hardest. Blizzard and NetEase haven't been as stupid as to sell them directly via a loot device or gacha, but what they've created is, in a sense which is more troubling. Legendary gems are only available from the bosses that are randomly placed in Elder Rift dungeons, and you can only guarantee that you will get a legendary gem by applying the legendary crest modifier the dungeon before you start it. The drop rates for legendary gems are very low.
If you don't spend any money on the game, you can only earn one legendary crest each month. Even buying a battle pass will only be rewarded with one or two more legendary crests every month. Beyond that, you'll have to buy them directly. Legendary crests work out at approximately $2 and $3 for each. The huge number of gems required to make the most of your character's equipment, especially considering the extremely low drop rates of five-star gems, is one of the reason the total cost to max out your character's capabilities in Diablo Immortal has been estimated at somewhere between $100,000 and $50,000 -in some cases, even more when you're deep into the system of gem resonance. (Rock Paper Shotgun comes with detailed cost breakdown which is on the more conservative end of this scale.)
Diablo Immortal has been given an extremely rough ride in this business model and perhaps in a way, considering popular free-to-play rivals such as Genshin Impact and Lost Ark have a lot of gacha mechanisms to draw in high-priced "whale" gamer. Diablo's renown and popularity with its core PC gaming audience, which has been built over a quarter of a century, is definitely one of the reasons. However, it's also true that this particular system is extremely problematic and the nature of buy Diablo IV Gold games could have an impact on that.