Prices in Next are, at most, similar to what they were @25 years ago, so you really do have to wonder. From the quality point of view, I've got a pair of deck shoes, made in Portugal, that I bought from Next in the mid 90's for £50-60. They're incredibly robust, and will probably outlast me. I doubt very much if the same is true for their current range.
I think you're right about that. This is where chains like M and S have really screwed up. Their basics, like shoes, socks and pants were always reliably good and mid-priced. But all retailers have chased the cheaper end of demand, so if you're in the market for a six-pack of socks for a fiver, then fill yer boots. The most expensive socks in M and S now work out at around 1.20 a pair. 12p a toe. No wonder they're rubbish.
But if you want socks that might last more than a few months, there's nothing until you get to the high end of the market.
Shoes is a good point though. Sixty quid was always my benchmark, and if you only want to spend up to that price, the choice is wide.
But if you want shoes that are any good, I've found that 90-100 quid is now the starting point.