You should make it so the players get black gems over time, not having to buy them (If thats the only way to get them). I dont understand why we have to buy them with real money all the time.
It's not the only way to get them; you find them in ruins -- from one to a hundred per ruin. You also get them from Salt Lakes (twenty gems per hour).
I get that the severs have to be paid for along with the staff but usually on average a beginner player finds 1-8 black gems in a ruin. Sure this would be fine if the artifacts per piece were also cheap at 100-150 bg but level 2 artifacts can be up to 7000 black gems and the higher the level the more the price is. So the only way to do it would be to drastically reduce the price of the artefact, increase the number of bg in ruins (bad choice) or enable player trading of artefacts to other players for black gems or other resources (which in my opinion is the best). The last choice could be made profitable for the admin by adding a tax amount of black gems like 20bgs for every trade.