Maplin have 6" digital caplipers on sale for ?9.99 till 20th March. Stock code N48AA. I assume they're the same as all the other Chinese-made 6" digital calipers.
The one I got doesn't look quite like the ones on the Maplin site, it has a silver rather than black scale, but the electronics bit looks identical. Doesn't feel as nice and solid as my similarly cheap stainless vernier caliper, but comparing a couple of messurements with a micrometer and the stainless vernier it seems to meet the claimed accuracy specs.
Now I just need to work out what an "electric pen" is, so I can avoid using one "for the fear of damaging its chip".