Sourcing Sintra/PVC Sheeting in the UK?

Does anyone know of UK suppliers of sintra/foamex/PVC sheeting or whatever is available on this side of the pond? Preferably an online store. All I can seem to find are hefty price tags in the hundreds which is certainly not cost effective compared to finished helmets you can buy. I'm planning on using 2mm for the helmet and gauntlets, and 5mm for armour/shoulder bells/kneepads, and use whatever's left to scrap up a jet pack with whatever greebles I have on hand. EBay has shown me 3mm and 5mm PVC sheet which comes to £40 when totalling up the amount of sheets I'll need. Is this a fair price?

Or would greyboard be a better cost effective choice for helmet/gaunts? I intend to wear it in bars so would like it to be pretty sturdy to handle a few knocks.

5mm Matt Foamex PVC Sheet 1220 x 610 White Matt Sign PVC Board 5mm 4ft x2ft | eBay

5mm 4x2 sheet for £10.49 with a one-off £10 delivery for any number of sheets bought at once.