While a girl maybe OK to fuck for a hour, possbily two, the realisation of spending 8+ hours in close proximity of someone who might start to get on yer tits is not a good one. Sleep or not.
I've done it twice, and on both occasions it was an agreed price. One was a WG, and the other was a Russian student who I'd started to date (sort of sugar daddy style, as I bought her dress and nice undies instead of paying her a silly fee - her ask). We had one overnight in a hotel in Kent, and another in a Travelodge in London for which I paid her £250, again her suggestion, as she was heading home to Novosibrisk the following day. She then went to a uni in Germany, and then lost track of her. As a student, she didnt have the hang ups some WGs have.
Neither would I spend a grand - plenty of WGs at £500 or less if you wanted an overnight.