The agency live-in carers that I use charge an extra 25% per day for an extra adult, but that would be someone not requiring care as such. This is when the client has a frail partner and the carer provides meals and does laundry for both of them. If two people require care then each needs a carer. Even one person needs more than one carer in the sense that carers need time off.
Unless the set up is providing care for a couple, you are effectively planning to set up a small CH. Imagine the red tape, training requirements, payroll, tax, inspections etc. You can't get round regulations, and neither should you, for the safety of the residents and the carers. It is not impossible to have a small CH with perhaps 5-10 residents, managed by an experienced person, but they still need additional staff to support them. Generally speaking, financial economies in care provision are easier to achieve in larger care homes rather than smaller ones.