Hi slim,
You may regret selling your old mailers, prices (as you have noticed) have rocketed over the past few years. I used to pick up baggies for cheap, even mailers could be had for £30-40 but nowadays your looking at big money.
They have been popular for a while now.
Other than the 3 pack mailers your looking at over £200+
The 16 pack your after if you could even find one would cost you an arm and a leg.