Sorry, can’t help as I am on Letrozole but that’s a bit of a problem isn’t it, when the medical advice is not to take it if you are lactose intolerant! I hope someone can advise more.
Price differences are often to do with particular brands or the deal a chemist chain has done with one particular supplier. Some people don’t experience any problem with different brands so shop around for the cheaper price, others find that the binders in both tamoxifen and letrozole brands can have an effect (and it can vary from person to person) so are willing to pay more for a specific brand. The active medicinal ingredients are of course all the same. Best wishes.