I got 4 mackerel from morrisons last week and they cost over £5.Always worth checking out the prices of fresh fish at your local supermarket fish counter and freezing it yourself before buying frozen stuff. Having said that, what you've bought does look cheap by comparison with a lot of frozen deadbaits.
I will invest in a vacuum packing machine. I won't be buying any next year as I do a lot of sea fishing. I only decided to fish for pike this year after all my mackerel had been eaten ?Its a good price as said, but there's times Morrisons are cheaper than that. I usually buy from there and vacuum pack in 2's or 3's then freeze them myself, vacuum packing will maintain their quality over to the following year without ice forming around them and burning them.