Every gem is the same price!

Null crystal-greatly increased damage, at the downside of everything else afterwards doing greatly reduced damage for some time.
Prodigy Crystal-enhances the mastery of the skill to which it is used.(you have mastery 3 ability the crystal upgrades it to mastery 4)
Shadow Crystal-it darkens your opponent's screen and also makes them deal 5% less dmg.
Glass Crystal-Makes block breakers do as much damage as they would usually do when block breaking.
Reap Crystal-stops all form of healing for a period of time
Inferno Crystal-your ability sets the enemy on fire
Terra Crystal-builds a wall behind the opponent, allowing him to be pushed into it and receive extra damage
Exponentiality-expands the timeframe between the hit and the damage that the opponent takes. It also makes the move deal 30% more damage.