OOOh that makes a lot more sense I thought it was applied for free. You might want to specify that.
Also homonymous secret? I think you mean the eschew materials one. And ya that would be a good idea. Most necromancers have a way to get free animate dead but its better to have this one have some cost.
Honestly I don't think the fiendish influence secret needs 20 ranks of knowledge arcana as a prerequisite. The fiendish template really isn't that strong. Or did you mean half fiend template? Because there is a world of difference between them.