as above, they are pretty expensive to buy new, but still expensive even second hand.
the site i worked at had a supair field permenantly in place for around 2 years and bunkers were left out through rain, hail, snow etc. however cleaning them down after every use saves the colour of the bunkers, and also make sure you have a repair kit for fixing any punctures as they are invevitable. deflating them and putting them away also prolongs the life and colour of them.