fish are worth what someone is willing to pay for them at the end of the day, they dont have a price like fuel or corn flakes do.
there seems to be a hell of a lot of people saying that the fish they own are 10 inch or 6 inch etc etc but they are not anywhere near the sizes stated. im not saying that you are one of them as ive never seen your fish and im not having a dig at you in any way shape or form but please could people get a tape measure and hold it up to the tank to get a more accurate sizing on their fish. ive been to look at several fish that have been sold as 6 inch and on arrival i find a 4 inch fish. its only 2 inches but it can make a hell of a difference if adding to an already established tank of 6 inch plus fish.
at the list you show in an lfs the red spot sev would be priced the highest and would probably fetch the most but privately i would say that about £15-20 maybe slightly more if they are the size quoted and are good decent and healthy fish but as i said a fish is worth what the buyer is willing to pay and also it will depend on how fast you want or need them gone.....