My daughter does ballet, tap, modern, jazz and acro. We pay termly, and the bill can range from £400-£600 depending on whether she's taking an exam - exam classes are extra and they usually go up to 2 classes per discipline in the term before an exam. We get discounts for multiple classes once they start doing 4 or more per dancer
The kit I don't find too bad. She's 10 now and has been dancing since she was 3. In that time she's had 3 ballet leotards - the change colour as you go up the grades - and 2 modern/tap leotards and tights. Tap shoes I buy on eBay as I know which make and style work for her, so I just buy the 2nd hand half a size bigger each time. Ballet shoes are about £10 - £12. Pointe shoes obviously much more, but she's not at that stage yet.
The big costs here are festivals (dance competitions) and costumes for performances. Festivals all have entry fees, and you need a costume suitable for each dance. And then private lessons to learn the dance. Lots of schools don't do competitive work, though, and it's almost always by invitation only, so most kids don't do them.
We do a big show every 3 years. My daughter had 8 costumes for the last one, varying from £30 - £60. They are fabulous costumes, though, and will be re-used for festivals.
Dance isn't cheap, especially if your child has talent and progresses quickly.