A good and healthy fish that is supposed to live several years actually is not a matter of pricing, is it?
I always would pay double or triple if I knew the trader is really reliable, it is not only to get Fish-Flesh that should flounder for some time, it is also a matter of stressless keeping and non-prior-damaging as well as support by a competent specialist.
Anything else in my opinion is just respectless consumption....
So 15, 30, 50 Bucks...it does not matter at all as long as the fish is kept greatly before!