Went to B&Q and bought a 5-man Gelert for £99, but it was too big when we put it up in the garden (we've got a massive Vango for long camping trips, we just wanted a quick-pitch weekender) so went back to B&Q and swapped it for the 4-man.
Haven't found this tent cheaper anywhere else. It was easy to pitch (under 20 mins) and with sewn-in groundsheet and pre-attached inner sleeping compartment, it goes up all in one go. And the bag is pretty small and weighs around 10-11 kilos. Quality seems pretty good and hydrostatic head is 2000mm.
Let me know if you've found anything easier/cheaper/better quality