Don't forget there's the cost of the vets call out fee.the cost of them microchipping and filling out the form,the cost of the microchip,and joining a society so you can get the passport in the first place!
I was told you had to use somesort of Passport agency and they all charge extra
I asked Pet ID but they only supply the microchip not the passport so to get a passport for my donkeys the cheapest is the DBS but you have to join the DBS to get a passport so thats the cost of the microchip+ the membership of the society+the Passport+the cost of the vet visit+the cost of the vet inserting it and filling in the form.... comes to about £100
Funny how you can get a dog or cat done for £15