This type of vice has been highly recommended by mini-mill users. It's similar to the 75mm "Pin type" vice at Chronos only it has very useful slots at the sides for mounting. I couldn't find the slotted type stocked in the UK except for one possible lead at over £100.
I took a chance and ordered one from a US eBay seller, for £47 including postage (would have been a bit more if I had been charged VAT and duty).
eBay item 330123775731.
The seller doesn't have any at the moment but may be worth watching. I think it's also available for slightly more from the US supplier Enco, but check it's the slotted one as many of their items don't have photos.
Dave