A few years ago, 700 quid got me some seconds insulated roofing panels 100mm thick. Some covered my 5x6m garage. Some more, when peeled apart, covered my 8ftx6ft shed. My 2ft x 12ft wood store. With two bits about 6ft long jammed between two sheds ready for when I find somewhere to actually use 'em . . .And the insulation from the peeled apart ones insulating under quite a bit of my suspended floor . . .