Prudie, if I were you, I would buy a quality brand of bins, but secondhand, still keeping within your budget. Then if you want to upgrade later you would probably be able to get very near your money back on the old ones.
I would for that money. I can afford to waste about £60. I'd prefer to try first but it would require a 45 minute minimum trip to the nearest town that would stock a decent selection, that's why I'm looking online, not seeing these as a long-term pair.
Thank you all for helpful and interesting answers. I should clarify that I already have a decent large pair at home, these are for taking away, they'll regularly spend 2 weeks in a beach bag (hence the sand). I'm going to continue looking online today with the new knowledge of the specs. I'll give BA to Baldric because he answered the actual question first.