Ed, I made 2 100mm thick bass traps, 2 50 mm first reflexion traps and a 100mm cloud. I brought some cotton dust sheets, 3 for £20 and used them as pillow cases, stapled them together and turned em inside out, and put the rockwool in, then tacked the top to the walls (ideally they should be on spacers to improve their efficiency). It works well, improves imaging massively, and tightens everything up a bit. I would buy about 2 packs of the wickes stuff to start out, make a load of 100mm pannels and maybe some monster 200mm bass traps, and back them with pegboard or some cheap sheet material to keep em rigid. It looks ugly as sin but it helps a lot.
Joe