I think Phil is spot on there. I do all the cleaning on new contracts myself for a two week period and then will supervise a cleaner/s to make sure everything is up to standard.
Often i'll offer the initial clean FOC just to get to grips with time and area and as a way of demonstration. I charge in the region of £13/14 an hour. This is based on what I'll pay on wages (+30-50%), and the cost of equipment (vacuum, mops, buckets etc) divided by the hourly rate over 12 months, if that makes sense. eg: Vacuum £100, 6hrs a week, 52 weeks a year = 32p an hour for the vac etc etc.
But I always give 2 prices, 1 with providing equipment and 1 without (just labour)