Yes, tax deductible. It’s like the difference between economy plus and first class on a long-haul flight though. The difference in price is so stark, it doesn’t seem worth it.
The other thing about that price differential, is that counsel who are best placed to afford the frizz top wig, namely commercial barristers, are the ones that will wear them most infrequently, as they are only required in the Crown Court, Administrative Court (Judicial Review) High Court and Court of Appeal. And not the Supreme Court notably! Oh, and fast and multi track track trials too tbf. I reckon most commercial barristers wear their wig and gown less than a dozen times a year, whereas a criminal barrister will wear theirs well over 100 times a year.