Hi simon and welcome!my uk freind
well to be honest preowned binoculars don,t come up for sale on the preowned market on more specialist sites like uk astrobuyandsell and seems to be mainly telescope oriented and any accessories associated around them.and unfortunately online merchandises like eBay can be a little bit hit an miss on occasions as you don’t know how well the previous owner has looked after them.however back in the day so to speak before I started spending obserds amount of money on telescopes etc,I used to own several pairs from Helios which I believe are Russian of origin.and thay really know how to make optics!,and as I recall thay offered nice sharp views for your money.you can find the range online with rother valley optics.
Helios 10x50 feildmaster £47
Helios 10x50 Nitrosport £87
Helios 10x50 Naturesport £90
Helios 10x50 mistral £120
Helios 10x50 mistral ED £149
Helios 10x50 Lightquest £309
As you can see! Bang on budget apart from one model and a wide range to choose from.