One of the things I wondered about in the earlier chapters was why did Miss Havisham request to see Joe about Pip's apprenticeship? Surely, I thought, it was none of her business. Pip and Joe come to Satis House and there is an embarrassing episode where Joe cannot bring himself to speak directly to Miss Havisham. No doubt if Pip's sister or Pumblechook had been allowed to come, they would have taken charge. Pip may have been almost as embarrassed by them, but he does not like either of them so at least he would not have felt guilty and ashamed about it. Anyway, after that, Miss Havisham tells him that Pip has earned a premium and counts out £25. £25 was a lot of money back then, especially as, so far as I can make out, Pip only went there on alternate afternoons for ten months.
(I am rather confused about exactly how long Pip used to visit Miss Havisham as a child because the time periods and the ages do not seem to add up. The BBC Great Expectations timeline says he went there for seven years, but I cannot find in the book where is says that and it does not seem right.)
I think the £25 was supposedly to pay for Pip's indentures, which he needed to become an apprentice. However, according to this link, Joe would only have needed to pay about £5.
I always had the impression that Miss Havisham quickly came to like Pip. It sounds like she wanted to compensate him well for inflicting Estella on him, as well as for being such a good guinea pig.