"all the local CMs get together" - I have to laugh. 
As our local CM coordinator, LA Early Years and SureStart coordinator would say, "we wish!"
Our delightful LA Early Years Officer, bless her, tries her very best to get us together. So far - well at least since I have been a registered childminder - we have yet to all attend the same meeting together!
I think what may give you that idea; one organisation in particular, publishes 'typical' or 'average' prices for the area. As a result, childminders like myself read this, and think OK then I will charge a basic rate £3.50 per hour. If all the childminders in that area do the same, it would give the impression that the prices are set.
What I would be suspicious of, is if all the childminders charged the same rates for other situations, for example, bank holiday rates, holiday rates, give the same discounts for siblings, all charge the same price for lunch etc IYSWIM.