Or,
"The holding in which the relic is held and displayed for the faithful produces additional regency and the province within it is blessed on the saints day; if the relic should ever be lost or stolen and not returned within a season the holding generates no regency for a year, the land suffers -1 prosperity for a similar time, and the temple regents suffers a minor loss of regency"
at a cost of 1 GB + 20 RP that's about equivalent to 1.5 times the income the province receives from the bless so maybe a bit cheap (the rp gain is probably useless as it is capped by bloodline).
The L8 version at 3* the cost could have the blessing for longer - but the loss if the relic was stolen would similarly be greater - say -2 prosperity, a major loss of regency for the temple master, and vulnerability of the holding to contest actions.
I expect that if the relic is guarded by a priest other than the regent, it would probably invite delusions of grandeur by the guardian a.k.a. Mr Great Captain.
I note however that effort in writing L6 and L8 spells is somewhat less well placed in a game with regents topping out at L14 or so than writing lower level spells. May I suggest
blessed land - converts the mebhaighl of the land which is otherwise wasted into a continual bless spell?
Haelyn's shield - neutralises arcane magic in the realm to free the people from fear of elves and suchlike? And of course the ever popular
purify mage?