At the price points you mention you are going to find it hard to find SPs around London who will include anal in a booking.
A few years ago it was more likely but since Brexit and Covid some of the older SPs have retired or don't offer anal now and a lot of the EEs have gone back home.
When it is still on offer then what I am finding is that the extra for it has often increased from £20 or £30 to £50 or more.
The three SPs you have mentioned are still active and have been reviewed by me in the past.
If you look at my reviews for the last few years you will find some others that are on, or close, to your target price.
Please let us know if you find any more VFM gems and let us have a review if you see them.
Regards,
davidgood