You can get significant differences in lining costs by the...

You can get significant differences in lining costs by the thickness of plastic you use...you can actually improve on lake pond recovery by using a very thin lining for a 10th of the cost compared with what would be required on land to prevent leakage / cuts etc. With ponds on the the lake it doesn't matter if you have some seepage from an enviro point of view. I suspect the EPA will want Kalium to use the highest grade plastic plus other measures which they may not have budgeted for in that $5.90 m2 figure.

Despite the speal from Kalium on lake ponds are better imo and you can line them pretty cheaply if you need to. It comes down to cost vs recovery.