Scrivener’s bloodmark will cost either eight crystal mana, if the ritual has not been mastered by the ritualist, or four mana, if it has been. You will most likely be required to pay a fee to the scrivener and to the mage/mages.
If the mage can’t solo cast it (has it mastered and has four levels of autumn law or just has eight levels of autumn law) then it will likely be a coven that you will need.
I was told by a veteran player that the usual fee is one to two crowns on top of the price in resources to perform the act or create the item. This means that if the other person in the contract isn’t willing to go halves you are looking at four mana (around one to two crowns to buy from a player) and two crowns at the very least. Four mana is quite a lot, being over half the amount that a player would get each event from their mana site.
Is this something you are willing to pay? I certainly wouldn’t want to pay all of that unless I knew the contract would make me at least a throne in profit.