No idea where it will end. In my opinion, they are stress testing the market with the fees to see at what point, people will decide to emigrate. It's awful.
This time last year, ILR cost less than £1,000 (£960 I think?), in April it will cost £1,875. There's every chance it could be £2,500 per application when your time comes (hopefully not!) if they continue to increase the fees at the same rate. Citizenship has gone up as well, but at least that is not required.