When creating the Gifts for EA#11, I did use the Talents and their costs from RMFRP Character Law as the starting point for many of them. However, I then tweaked things, adjusting the costs for the basis of the power levels of the gifts, trying to balance them against one another.
So, if you are going to create/add new Gifts, you should use the existing ones from EA #11 as your starting point, and determine the costs accordingly based on how they stack up against new Gifts.
And keep in mind that if it it is something that everybody is likely to get, then upping the cost a bit more is maybe a good idea.