Hi Smudge,
Depends on the condition of the action and metal work - Replacement pattern sights will cost about £55.00 unless you can find some 2nd hand ones. Check that the sight dovetails aren't mashed.
£ Value wise to the collector it will be a bitzer, if it has a Bsa stock off a later model.
However, due to these old Bsa's having lots of interchangeable parts, they were fixed up over the years with what ever was available, so its still an interesting and collectable rifle and in its own way historically correct !
If its a good shooter in working condition, as a project gun it might be worth £45 or so. Though its value as spares will be slightly more.
Cheers Morgan