There are a bunch of decent ones around for less than £100.
What sort of welding are you doing? Just about everything will cover MIG and Arc (but the eBay specials are worth avoiding). TIG is something the really cheap ones don't cover, and they start at around £50. For micro plasma welding the budget might need to be over £100. Why the £100 price?
Nice. If you have the budget for a 255 then the red SWP mask, or the ESAB Origotech look quite sturdy and ought to be nice to wear. I've got an eyetech II 5-13 myself which is lovely, and there's a 9-13 shade version that should to come in at about £100. I think BOC also do a version of both.
Sub £50 masks would be fine for MIG too, but their cases can feel a little flimsy and the viewing area can be small. From there it seems to be nicer cases, TIG capability, and more features, though I haven't used half the features on mine.
I may not be able to afford one so am thinking of buying the one on the far right – anyone used one of these? Fifteen quid difference is a decent overall and not to be sniffed at.
I may only need it for the winter – van resto – and would probably put all my recently purchased kit up for sale come the spring, to recoup some of the expenses.