This is the cheapest I've seen so far, at Sainsburys
https://www.sainsburysentertainment.co.uk/en/Films-TV/Blu-ray/Daniel-Radcliffe/Harry-Potter-The-Complete-8-Film-Blu-Ray-Collection/product.html?product=E10990376
https://www.sainsburysentertainment.co.uk/en/Films-TV/Blu-ray/Daniel-Radcliffe/Harry-Potter-The-Complete-8-Film-Blu-Ray-Collection/product.html?product=E10990376