There are Chinese copies* on eBay at around four quid, but they look a bit rough. As bizarrely expensive as the US ones are, the material is top class stuff.
*a 'spring punch' search will bring them up.
There are ones out there that will take a masonry nail as a replaceable point.
I would say that, for site use, as the nail-punches would probably be used, they are a very 'losable' item, and it's no fun at the full price.
I'm also a fan of having a square somewhere on things than don't need to be fully circular.
Screwfix are good for what they're good for - and there's a shop at the end of my road now, so no 'building an order' is necessary..