If you are offered a 90cm for €30 it is probably not the best quality and will not perform as well as a better quality dish. Good makes that I have used are Gilbertini, Fracarro, Triax, Visiosat, Hirschmann, plus some others, but unfortunately there is a lot of un-named garbage floating around.
Depending on which receiver you intend to use, it may be worth motorising the dish, then you will have access to a lot more than the British channels.
