Seems reasonable to me, although you don't say how long the booking will be. It is not an unusual price for a duo, especially if a level of kink or special service is involved. Especially if the price includes the hire of the venue and the SPs will not be able to spread the cost over a number of meetings like thay can at a hotel. Given that you know the SPs, or at least River, and you can be pretty sure of getting what you want, then you should be OK.
However, I admit that I really enjoy your reviews Colston, and want to read about what you get up to, so I might be biased!