magnetic right angle clamps

[Rabs]

No. £12. For 2 of them.

Huh?  How do you work that out?  Pack of 10 magnets for £4, 2 magnets per part (or 4 per complete clamp). And there are even cheaper places to buy, such as: http://www.ebay.co.uk/itm/10-x-Very-Strong-Square-Block-Neodymium-Magnets-5mm-x-5mm-x1mm-Fridge-/290720620581?pt=LH_DefaultDomain_3&hash=item43b04ca025
£2 for 10 magnets.

My scrap plastic doesn't have magnets in it - and I couldn't cut it square either.

Ok, then perhaps the DIY route isn't for everyone but I suspect that most could manage the use of a set-square.  And even if not, it doesn't really matter - only the magnets need to be at right angles, everything else can be almost as scruffy as you like.  You just need to glue them overhanging the edge of the card slightly:
[smg id=10379]
Then it doesn't matter how wonky your cutting is.

[ParkeNd]

No. £12. For 2 of them.

Huh?  How do you work that out?  Pack of 10 magnets for £4, 2 magnets per part (or 4 per complete clamp). And there are even cheaper places to buy, such as: http://www.ebay.co.uk/itm/10-x-Very-Strong-Square-Block-Neodymium-Magnets-5mm-x-5mm-x1mm-Fridge-/290720620581?pt=LH_DefaultDomain_3&hash=item43b04ca025
£2 for 10 magnets.

Simples!! I bought some from York.

My scrap plastic doesn't have magnets in it - and I couldn't cut it square either.

Ok, then perhaps the DIY route isn't for everyone but I suspect that most could manage the use of a set-square.  And even if not, it doesn't really matter - only the magnets need to be at right angles, everything else can be almost as scruffy as you like.  You just need to glue them overhanging the edge of the card slightly:
[smg id=10379]
Then it doesn't matter how wonky your cutting is.