User blog comment:ClariS/FEEDBACK! Cost Efficiency/@comment-1618239-20130110070440

I might estimate spell vamp as being of equal gold value to life steal.

It's not quite accurate, but basing the value of a stat off of the recipe price of Revolver is probably inappropriate seeing as Revolver is an advanced item, which in LoL means it's slightly more cost-effective than a basic item.

I dunno though. Vamp sceptre being an advanced item kinda messes with things.