I promoted in 2010 to 1st Dahn, the fee for me was $300 and included a certificate, ID card, Uniform ($120 if purchased from organization separately), and belt with gold thread embroidery. I felt the fees were reasonable and do not regret having paid it.
Ostensibly so that the head of the organization and/or his #2 would see you on the mat to verify that you're performing as you should, for your rank. They toured the country to visit each school every year (they each came to my state once a year, anyway). I question how much time they actually spent with individual black belts, but that was the explanation.
I'm testing for second dan on Saturday, for which I will pay £25. Naturally I'm quite happy with that!
When I tested for fourth dan I was told it was going to be $600. I said fine I'll just stay at third dan, no big deal but I would no longer assist with classes. I was told I HAD to assist with classes to continue to train but I refused and would continue to pay my $120/mo fee's. About a week before the test I again was asked to test, I said no fee if he wanted me to help teach and he finally agreed. Depends on the school of course but sometimes you can negotiate the fees charged.
My eighth dan test was $850 plus airfare and hotel room cost. This was six days and four nights in the field meals and all events included as well as the judges panel. It was a multi-style exam that included TKD, but not restricted to it.