Why not simply introduce an enhancement attribute for Simony that reduces the silver costs per scroll by 0.5% per attribute level, and when maxed by an additional 10% like all enhancement attributes?
If it’s combined with a reduction of Parchments required per skill scroll (since you can only craft max level skills now, you need 5 -15 Parchments), maybe to something like
skill level of the skill you want to scroll * [ 18 / Pardoner Class level] amount of Parchments per scroll, rounded down
the scrolling system could become an effective silver sink while retaining the investment requirement on the Pardoner to be efficient (i.e. the character needs to be leveled to Class level 45 and have 103462 attribute points put into the Simony attribute for maximum efficiency).