Just a suggestion, but I think you might be able to re-use wigs a lot.
I mean, I see a lot of black-haired characters in your list. You could probably just buy 1 or 2 black wigs and style them differently for different characters.
I do that all the time, if I already have an appropriate wig at home I'll style and re-style it for a range of different characters. Great way to save money.
Good luck searching for those wigs!