Animate dead is one of the few spells which has a variable cost to its casting, as it's based entirely on the amount of HD you are going to raise with the casting, which is partly dependent on the CL.
When you scribe a scroll, all its costs are paid up front, both for the scribing and if there are expensive material components.
So a cleric/wizard base animate dead scroll costs 375 plus x25.
How would one who finds or buys such a scroll determine how many HD it's able to produce? If one was to create it themselves at the lowest cost (400), does the scroll restrict the amount of undead HD it can raise?