If you are going to go down the BDM route, I think it would be wise to get one that knows your industry inside out.
You really want him to get leads, follow leads and close deals and have a proven track record. There is not much point in him getting leads then passing them on to you to quote and close them, especially on a wage. He will be basically doing a cold callers job.
If he does start pricing work that he knows nothing about, you could well end up with whole stack of under priced work that you will ultimately have to look after.
If you pull someone in from within the cleaning industry, he/she will often have a 'little black book' of clients that can be called on immediately.
Have a look at this company, they have a good list of contract cleaning BDM's in all areas with CV's and track records.
If you give them a call they will send you email updates when candidates come on the market.
www.humres.co.uk