I just bought some brill cheap window fly screens from this website only £3.99 each and you only pay £3.95 shipping!! I bought a few rabbit food bowls too and still only that for shipping - mason cash bowls are heavy too!
http://www.petcompany.co.uk/acatalog/Pest_and_Insect_Control_and_Miscellaneous_Items.html
http://www.petcompany.co.uk/acatalog/Pest_and_Insect_Control_and_Miscellaneous_Items.html