As a general rule I agree with Low'nSlow.
CAA Permit fees aren't particularly high although they are higher than the PFA fees.
AFIK a Permit is a Permit is a Permit. PFA and BMAA are both organisations approved by the CAA to issue permits for aircraft for which they hold approval and there is no difference in the rules whether your Permit was issued by the PFA, BMAA or CAA.
There's a bit of infighting going on in some quarters at the moment between elements of PFA and BMAA but it seems to be more among the members than the executives. Some seem to think that the organisation that was responsible for getting a design through approval should have sole rights on Permit renewal. I don't subscribe to that view any more than I would to the view that the Type Certificate holder should have sole rights to CAA renewals.
The idea that a permit allows you to save a packet by doing the maintenance yourself is based on a bit of a misconception. There is a list of maintenance items that a pilot can sign off on a Permit that is marginally longer than that which can be signed off by the pilot on what used to be a Private Cat C of A. Anything more than that can't be signed off by the pilot. There is of course nothing to stop you doing the donkey work yourself, whether it is on a C of A or a Permit providing you have an engineer willing to sign off your work.
In our case the engineer produces the worksheets detailing what needs to be done (inspections, checking mandatory mods etc). We do the dismantling and cleaning, he does the inspection, we reassemble and he signs it off when he is satisfied. (we're on a PFA permit)
Hope this helps
Mike