Hi,
I have done something similar for a letting agent. It was a two bedroomed flat, not been cleaned for several years by the state of it. And the carpets needed cleaning aswell....
At the time it took two van loads to take the rubbish, old clothes etc away and i didn't have a small van at the time, it was a large Toyota Van....
I think I charged around the £350-£400 to do all the above. This was around 2 years ago!!
So with that in mind, you need to do as the two Martins above have suggested, and that is to go and visit the property in question with the housing rep and decide if you feel it would be worth the hassle and time compared to the money you would want to charge.
As Martin has suggested, the walls may well need washing down, everything needs to be sanitised, it sounds like too that the Carpets will need cleaning and sanitising too. The time to bag up the rubbish and take them away for disposal will need to be considered too.
It will take longer than you think, so add on a couple of hours to your estimate. And if you can, try and have two or three cleaners with you, not only to help get it done quicker, but gives you moral support over the long hours compared to being on your own.....
Worst case senario:
Carpets cleaned and sanitised throughout £150
Staffing if you can around £180 per day
Disposal of rubbish - Many sites wont take Commercial rubbish £
Materials, chemicals £
Plus you are in it to make money for yourself - Profit £
Looking to charge around £450 - £500
Hope this is of help as a guide etc....
All the best, and you will have to update us on how you get on or if you don't take on the job.
Regards
Tim