Too many variables to answer that.
How long have the houses been on the books are we talking years?
How do they pay ?
How well priced is it ?
Are they trad and need switched to wfp?
Rounds go from anywhere to x3 the monthly value to x6 or 7. Some even more.
The honest answer is it's only worth what someone is willing to pay. If there's more than one after the round the price will go up.
Personally for me to buy a round every last box would need to be ticked. Every house would need to have been getting cleaned for years and already wfp, no collecting, well priced and extremely compact. Oh and they all paid on time.
Anything less and the rounds value goes down and you would probably be cheaper hiring a canvasser.
My experience of shops is that they will drop you instantly if a cheaper cleaner comes along.
Sorry i cant give you a figure but their really isn't one.
Back in the day 20years ago the going rate was round my area (Yorkshire) was pay the equivalent of 2-3 months worth of the work and it’s yours. No idea if that’s changed.
I’ve known people here (Cornwall) “rent out the work”. And I was disgusted to find people were self employed, used their own van and equipment and still paid 50% to the work owner.
But that was taking advantage of young ones I think. If I still did window cleaning I wouldn't work and pay more than 20-30% commission if I used my own van etc. It’s just not right IMO.