Generally speaking from a cost perspective if I need to create a blood bullet wound on an actor's forehead can it be easily done in After Effects / Post production or should I hire a make up artist for the set? Thanks.
Create a feathered mask and add a blood splatter image. You can easily find many tutorials for bullet shots on YouTube.
Practical effects almost always look better than doing it in post production. Doing a convincing job in post will require a skilled After Effects designer.
If your budget extends to hiring a makeup artist, I'd do that. But, if not, there are some quite good tutorials around for this kind of thing, like this one: