The price you see should be the price you have to pay. Any non-compulsory fees etc (eg paying by credit card) obviously shouldn't be put into the overall fee unless the airline gives you no choice other than to pay those fees.
I have no problem with airlines giving me a full breakdown of how the fare is made up when I come to pay it but when I search for the cheapest flight I want to be able to see it without having to go through the whole booking process.
When I buy petrol I don't see the price as being 20p per litre and then when I go to the till it magically becomes 96p per litre. When I buy clothes I don't see a £10 t-shirt becoming £11.75 at the till so why should it be any different with flights?