[bagels]

That is an understatement. Mushrooms are one of the least calorie dense foods. It'd take something like 20 lbs. of mushrooms to hit 2000 calories.

[swiftcoder]

On the flip side, they are absolute flavour bombs, and often on a budget you are short on flavour-enhancing ingredients.

Forage them (safely!) in the fall, dry them out (I stick them on a wire rack over a radiator for a few days), then into an airtight jar. Toss a few into soups/sauces the rest of the year.

[BigGreenJorts]

I'm assuming the mushrooms are for micronutrients not calories. A couple of cremini (just the mushroom I buy most and speak to) have all your copper needs for the day