The break down, 
What I have done here is for the first time is using Nicks Spread sheet he kindly sent over as a test. I must say it work out ok, but like I said you would need to add on Supervisor visits, travel, admin and other overheads you may have.
Its like anything, if you want it, it comes down to Price. Go in lower if you really want it. And throw in some services the others are not offering.
We win alot of contracts just because we throw in freebies. like liquid soap, air freshener or window cleaning at a very huge discounted rate. We have WFP and tradition cleaning systems and even Carpet cleaning. 
If you want to be competitive with the BIG Boys you need a large number of contracts. Most on there own are making a loss. But overall are onto a winner. The large companies spread running the cost over several contracts.
Once again you will win it on Price and what you are offering. You need to be the lowest priced and have the better specification. 
Rate of Pay                                     £5.85
Number hours per week                    10
Nett Employment Costs                    £58.50
% Allowance Employment On costs    10%
Weekly Employment Costs                    £64.35
Annual Cost   
Nett Annual Cost (x 52 weeks)   £3,346.20
Holiday Pay   
Number of weeks   4.0 
Holiday Pay Cost    £257.40
Gross Annual Labour Costs                   £3,603.60
Gross Monthly Labour Costs (GLC)   £300.30
   
Cost of Equipment                                  £100
Contract Term                                 12 
Monthly Allowance                                 £8.33
   
Cost of Cleaning Consumables    
Percentage (of GLC)   2.50%
Monthly Cost                                 £7.51
   
Other Costs (Uniforms, Insurance etc)   
Percentage (of GLC)   2.00%
Monthly Cost                                 £6.01
   
Net Monthly Cost of the Contract   £322.15
Profit Percentage   19%
Monthly Profit Margin                  £59.60
Monthly Contract Price                 £381.74
Annual Contract Price                  £4,580.93