Assume I have a card that has the effect "Gain X hp per turn" and its cost is Y quanta.
How much should a card that has the effect "Gain 5X hp" cost?
How much should a card that has the effect "Increase your max hp by X every turn" cost?
How much should a card that has the effect "Increase your max hp by 5X" cost?
How much is Y in respect to X?
I would start with the assumption that a card that heals 5X per turn would cost 5x* the amount of a card that heals X per turn. This is not always true because healing per turn is less effective at really small or moderately high quantities.
*5x the cost does not mean 5x the quanta cost. 5 photons cost 5 cards ~= 8
+ 1 card.
Next I would use a comparison to an existing card.
Druidic Staff costs 2
+ weapon + 1 card for 2 attack and 5 regeneration.
Shard of Gratitude costs 5
+ Mark + 1 card for 5 regeneration.
Both of these can be reduced to 3
/6
+ 1 card for 5 regeneration.
So X regeneration would cost X-2
+ 1 card or 1.5(X-1)
+ 1 card.
Next I would compare healing to gaining max hp.
Heal 3
+ 1 card for 20 healing
Shard of Divinity 5
+ Mark + 1 card for 24 max hp
4X healing costs (X-2)
+ 1 card
5X max hp costs (X-2)
+ 1 card
This implies that max hp is worth slightly less than healing. This is counter intuitive. Healing enables Elemental Mastery. Max hp healing is cut off at 500 rather than 100. I would hazard a guess that Shard of Divinity is slightly more powerful than Heal. This sets max hp gain and healing at equal value.
So X max hp per turn would cost X-2
+ 1 card or 1.5(X-1)
+ 1 card.
Note there are some assumptions that should be double checked.
1) When is healing not linear? (heal 500 is less valuable than 5x heal 100)
2) When is max hp gain not linear?
3) Are the cards used in the comparison balanced?
4) What is the relative balance relationship between Shard of Divinity and Heal?
5) Is the relationship between max hp and healing different from the relationship between max hp per turn and regeneration?