Re the airbricks, have you actually looked to see in heavy rain if water is pooling outside them and getting in to them? i.e. do you know that they are actually causing a problem?
If water ingress is an issue, and you want to save money, I would imagine there is a solution where you could block/cover off say the bottom two rows of holes in them, making them watertight, so you could withstand a higher pooling depth, but still have some ventilation.
I guess it depends on how much money you have to spend.