diso life on a CAA Permit will mean an annual inspection by a CAA engineer who may or may not be familiar with little aeroplanes in general let alone you model in particular. Read EXPENSIVE, I think they charge around 140 quid an hour(???)
I have no idea what an EASA Permit would involve but I can't realistically see it being less complicated than a CAA Permit.
The PFA Permit allows you to do virtually all the maintenance work yourself as long as it is signed off by (and preferably supervised by) a PFA Inspector who will be a lot cheaper than a CAA Inspector and very probably more familiar with your type of aircraft.
If you chose to have an engineer do the work then the cost differential will probably be negligable unless you use one of the more expensive maintenance shops. The big difference will come in the near future when you will HAVE to use an M3 licensed facility to do your Annuals / Star Annuals. That will be a lot more expensive than using a PFA Engineer / Inspector to do the PFA Permit Annual.
I used to operate an L4 Cub on a Permit and there is no practical difference in the operation of my Auster on a C of A. I fly for fun, no IMC, no night and with a 59 year old engine I avoid built-up areas anyway!
Regarding hard to obtain spares, the PFA take a much more pragmatic view of manufacturing new spares. I have found their engineering department to be far more responsive than that of the CAA. I am not complaining about the CAA in any way it's just that the PFA is better set up to respond to the little guy's pleas than the CAA.
Overall I would guess that your aeroplane would be better off on a PFA Permit (as long as your flying pattern is similar to mine) and will probably be worth more and easier to sell.
PS Have a look at the Auster on a Permit thread running concurrently with this one.