Hi James
You'll need 8ft X 4ft sheets
That price is very steep
Parkers is probably not the best place to buy alloy sheet ..... There is a lower cost national company out there ..... Be buggered if I can remember the name of it at the moment
Just for reference .... I collected 2 sheets of 1.2mm & 1 Sheet of 2mm of half hard alloy sheet from my local general steel stockist ( Not the cheapest of places ) !!?? ..... Cost me in the region of £125 inc Vat