I managed to get some in a sale in Debenhams a few weeks ago for about £7, they are fabulous! Have a look in TKMaxx, I've bought several pairs of Falke tights for a fiver or so in there. They do have some funny colours but if you search you can usually find a bargain
I have the Falke opaques. I bought a couple of pairs last year and based on that a couple more this year. They are fab. I wear them almost all the time. Wear well, wash well, not prone to holes and ladders. Very comfortable. Properly opaque as well.
They do seem unreasonably expensive compared to say M&S, but are so much better imo.
I thought paying £29 for tights wass a bit mad but they are worth it. They are lovely and soft, have a proper gusset ( comfy), properly shaped toe and heel, and a wide waist band. They feel as warm as trousers and much warmer than cotton leggings.
They are much nicer than both Autograph and J Lewis equivalents which IMO are a bit skimpy in the sizing- I'm a 10.