I used to do lots of showhouses, going back over the last 20 odd years, sometimes 2 or 3 per evening, or up to 4 a day.
I only do the occasional one these days, and charge from about £120 for a 4 bedder, but this depends upon condition & travel time.
Most of them are extremely lightly soiled, apart perhaps for the hall & stairs, and the job can be completed very quickly. For most areas it can be just a brighten-up job, & on the very odd occasion I have done two 4 bedders in a total of 2 hours, and would rarely expect to spend more than 2 hours per house. I very rarely vac as the very efficient contract cleaners will have been in not too long before.
Bryan