£90 a term sounds like a lot to me for 1 class a week. I have dd1, who is 11, on a special program at her dance school and pay £288 per payment session (we have 4 payment sessions a year).
That covers all her classes and gives her reduced private lesson fees (we pay £12 per half hour private lesson as apposed to £14). She does everything going. Ballet (5 classes a week), contemporary, modern, jazz, street jazz, musical theatre, tap, Classical Greek and body conditioning.
That said we aren't in London, we are in deepest darkest devon.
Exams vary from £20-£120 (£120 would be a major, vocational exam).
Shows we hire costumes. Festivals we can hire or buy ourselves or even make. Dds last tutu cost £120.
Festival entries vary from festival to festival. Some are £3.50 a solo, some are £5.75 a solo.
Leotards can be picked up relatively cheap, or second hand. Shoes can be got from dance direct for £6. Pointe shoes (if she gets that far) are another story! £50 every couple of months by the sounds of things!