I agree with others, do not save on school shoes because you will be amazed at how the shoes will be just after the first week
I spend a little fortune on them but i do not have to change them unless they dont fit anymore. They tend to fit until April-May.
For trainers i buy good brand for the same reason and last year they lasted until June. Buying in sport direct is a good idea as there are always good deals.
I dont buy wellies anymore as we use gore tex walking boots now which can be used jn any weather anywhere (we walk a lot). But asda has very cheap ones if you need wellies.