Hi Mike,
First things first!
What are their present arrangements?
You need to know and understand this because TUPE, may well apply to their current cleaners, which may have a huge impact on the quoted price.
You seem to be pretty certain of both the timings and the staffing side of things, so I assume that you have carried out a detailed survey of the client's premises and agreed the cleaning specification is acheivable within the current timings/staff levels.
OR The client has informed you that they want 2 x cleaners for 2 x hours each per evening.
If you have carried out the survey, and are sure that you can attain the standards required by the client, great, you are half way there!
If, however, the client has informed you of their own needs, you really do need to look into this in a bit more detail, asking questions, about the need to change contractors, quality, reliability issues etc. This will enable you to ascertain if the contract is actually do-able within the current time/staff limitations etc.
Your costings should allow for holidays/sickness etc.
As for your first thoughts on costings, in todays market, and assuming that there is no special equipment needed I think that you should be looking at an hourly charge of between £12 to £15 per hour + consumables.
Hope this helps, and best of luck!
Regards,
Rob