£0.
Regularly after I've washed it I flip over and cut the ends off. Then if it feels shorter, which it hardly ever does, I look at the back to see if I have to straighten anything out.
I have straight long hair so it's v. easy to manage/ignore. Too anxious for hairdressers, plus they use lots of products which I'd be afraid would aggravate the dermatitis....yucky condition.