We do not buy potato starch.
We cook at home from defective potatoes after sorting (cut, gnawed by a bear, and the like), from last year’s wrinkled old.
So they would throw it away, but it will do good.
Potatoes need to be peeled, grated, add some water, mix well and squeeze through a frequent sieve.
This procedure must be repeated more than once.
The starch will settle out in the water.
Drain the water, and dry what remains in the oven under a thin layer until the moisture has completely evaporated.
Cooking at home is a household chore.
Save a little here, save a little there, and, as they say, a penny saves a ruble.