If you look across the various platforms, from AW to agencies, the prices for dinner dates range from £500/£600 to a few thousand. It is really up to you how much you want to charge. It is also worth considering that those who want dinner dates make up a tiny proportion of clients, so you might get one or two a month, or none at all.
I only offer dinner dates (or shorter drinks dates), four and three hours respectively, although most run to five hours. As I only charge for my time, (yes, that old chestnut), I charge what I would charge for three or four hours of non-social time. (I have my own website and do not use AW. I also do not provide the hotel, that is entirely on the client.)
I think what is important is how you pitch yourself, and besides, you can always find clients who will pay your prices, so maybe it is worth just going with the flow, starting with a price you feel fair and then adjust accordingly if needed. £750 which you have mooted is an ideal place to start. If you use AW, I think it is pretty well-pitched, particularly if you’re providing the accommodation. However, I would only recommend this in London as I am not convinced you would get many takers elsewhere.