Writing a scroll of defense with my L49, literacy 100 gnomish bard using a blessed writing set and a cursed blank scroll lowered my mana stat from 19 to 1. That's a BIG drain! Apparenly writing on cursed paper is a really bad idea, but it made sense to me at the time, since I wanted a cursed scroll.

I think that the mana drain from writing most scrolls should be capped at 4-5 or so, maybe 10 for SoCR. That's still a really hefty cost!