This chicken ark is £215. There is a website called ideas4pets. something?! that has some very cheap henhouses, but they are known to be a bit flimsy and the runs are tiny.
Unless you are going to let your chickens out daily to scratch around the garden, always get the biggest run you can afford and only put 2/3 hens in it. Seeing chickens running along the wire mesh, desperately trying to get out, is not nice.