I took my DDiL to R&P to be fitted for a bra to go under the wedding dress I was making for her. It was done by eye and fitted perfectly. I was looking at the portrait of HM and said I reckon she's a 36F, the assistant looked at me and said you can have a job here anytime! Apparently it's a state secret and only one person knows, but all the others concurred with my guess.
I once worked for an Italian lingerie company, and when you are doing it all the time you get to be able to guess a size. I was invariably correct.
I have quite a few friends with awkward sizes, big and small, and swear by R&P.
I cannot understand the objection to paying a lot of money for a bra that fits and is comfortable and worn every day. I am fortunate that although a 95E I have found a bra in French supermarkets that fits me perfectly and is usually 22€ or less, with lovely matching knickers. I have loads of them. I do believe in having a bra that matches every outfit. Why not? And pretty, it's the feel good factor. If necessary I wouldn't hesitate to go to R&P - just have less of them!