I don't know any face-to-face tutors. I imagine there are plenty here that could be interested if the price is right. I'm a course leader for advanced Excel topics. So whilst you say you realise that it will be expensive, are you aware that the cost is probably in excess of £50 per hour? And I reckon that's cheap. Excel tutors tend to gain income through numbers - i.e. a per delegate fee. And are you also aware that it takes time to learn Excel properly, even with a dedicated tutor, and so the cumulative cost will be substantial?
Personally I think the very best resource is right here - i.e. the forum. Start asking questions and better yet answer other peoples questions. This is pretty much how the vast majority for talented Excel users learned their skills. Of course a good book or two is also very helpful. We can definitely recommend appropriate titles, depending on what specifically you want to learn. MrExcel has it's own library of books that you can pick from. I would put that money you have aside and invest in a bunch of good books. I'd attend a seminar or two - and beyond that I'd just knuckle down and try and study as much material as possible and put that learning to the test here, in our questions forum.
I'm afraid we don't allow soliciting on the forum so I cannot allow anybody to put themselves forward (not at least without the consent of the other mods and admins). But I'm happy to keep the topic open because others may weigh in with alternative suggestions that could help you determine the right path to gaining the expertise you need.