Peanuts are cheap, but they aren't the best for squirrels. Peanuts are a legume and legumes are on the "Do Not Feed List" for squirrels. Legumes are high in phytic acid which can bind to calcium in the digestive tract and block its absorption.
Almonds, walnuts and pecans are better choices. Check out
www.anuts.com, it is a good source of nuts in the shell. I have purchased nuts from them and have never had a bad nut. Aesthetically they are probably 'seconds.' Some of the almonds shells are chipped, for example. The packaging is simple. However, I don't think a squirrel cares about any of those things.
Prices are low, $2.27 for English walnuts and $2.47 for California almonds, currently.