What is the most cost effective way at home to dehydrate nuts?
Most dehydrating is about using as little heat as possible to dry the air out without cooking the food.  On dry, sunny days, you can use the sun on a dark surface as a heat source.

Dark surfaces will absorb heat from the sun, heating the air which will lower the relative humidity and and warm the nuts which will 'mobilize' the water in the nuts so the air can carry it away.


If you have a dark enamel pan, put a single layer of nuts in the pan and leave it in the sun for a few hours.  Keep an eye out for hungry birds!
If you have a black outdoor grill that sits in the sun, place a single layer or nuts on a pan or sheet of foil, and close the lid.  Check every two hours.


Total time to dehydrate will vary on many factors including the season of the year (angle of the sun), outside temperature, relative humidity, type of nut, etc.

Because of the additional exposure to spores in the air, the nuts should be used before they can mold, usually within a day or two.  To discourage mold growth, don't store the dehydrated nuts in the dark.