Certainly for fuel, AVCARD is now owned by world fuel service and is cheaper than the typical UVAIR/BP/SHELL cards, I paid a little over 39p per litre at EDI the other day and thats at $1.50 per pound . I needed to allow 4 hours as they had to find me a gap from the main apron and I had to take 2500 litres+ but it was 30% cheaper than everybody else.
Im amazed by how many crews allow the handler or even worse the fueller to decide which carnet they use.
Its possible to earn free handling just by handing over a different piece of plastic - I saved well over 300 quid that day