In addition to diagonal57. It is not essential that the same make of tyres are on each axle, but I'd recommend it. Different makes and treads grip and disperse water differently, and I like mine to all be the same. But that's personal preference.
Why do you have to get a minimum of 2 done? Can't the puncture just be repaired?
There's certainly no reason why you would need 4 unless they are worn out.
The price of tyres depends hugely on what make of tyre you get and what size they are. Different Fiestas of the same year could easily have different tyre sizes. If they are fairly standard than a budget make tyre shouldn't cost much more than £40 fitted.
Don't go to Kwik Fit whatever you do. Go to a decent independant dealer and do buy a premium make like Michelin, you don't need it and it'll cost you silly money