Just having a quick look on AutoDoc, there £35-50 plus delivery, not sure if any are from the same manufacturer as OEM though. I'm a bit reluctant to replace knowing the same issue will just reoccurring before too long.
Interestingly, the product descriptions all say "silencing material", no mention of heat insulation. If it's an easy way to increase engine sound then I'm in, but is it worth the risk of potentially damaging the paint..?