In my TEDxToronto speech (Preserving Food: You are What You Eat) I mentioned preserving red peppers in the fall. I claimed we save $100 a year. A bushel of red peppers weighs around 30 pounds and is worth around $20 in the fall (you can buy them at farmers stands and European grocery stores). Red peppers can easily reach $4 a pound or more in the winter so the bushel would be worth $120 if bought individually.
You can preserve the lot in about an hour (with less than half of that time actually requiring you to work; the rest of the time you are waiting for things are can do anything else).