My company carries out work for a large letting agent, my advice would be to view the properties first, we get given the jobs with details, if carpets need cleaning, rubbish removing etc, we get to the property and ring in a price, they are very very good earners, most are check out cleans so the payment comes out of the tenants deposit.
I would never agree a price for an end of tenancy without seeing it first, each are individual, good and bad. I charge a minimum of £100 plus vat for an easy 1 bed apartment this would consist of a general clean, all kitchen cupboards inside and out, appliances etc, 2hrs max 2 cleaners.
Regards Paul