I can't imagine that the european releases of TNG will exceed 50 euro's/pounds per season. Paramount keeps the prices of their BD releases high, but any higher than that would be rediculous.
I'll bet about £80 per season. You have to remember that when the 1-10 movie boxset on Blu-ray was initially released, it retailed at £120 in the UK. OK, it's come down since then. . I got it for £75 last year.. .Now that set was 12 discs with minimal work needed to produce the content of the discs.
TNG will presumably be 7 discs per season, but with the huge costs of HD production needing to be recouped. Paramount knows that Trek fans have been chomping at the bit for HD TNG. Many of those fans will more than likely pay pretty much anything for these sets, and I suspect they're going to have to. As I paid full whack for all the DVD sets on first release, I think I'll be obtaining these if and when the HD rips appear on torrents.