I made the same mistake I did with the broccoli, by purchasing more spinach (2.5 lbs) than I could eat within a week or two at most before it goes bad. To not be wasteful I decided to to freeze some of the extra.
Start bringing a large pot of water to a hard rolling boil, add as much spinach as you can fit and cover with lid and cook for 2 minutes. Strain into colander and spray with cold water for one minute to stop cooking process.
Allow water to draining out for a few minutes then squeeze out excess with your hands and lay out on some paper towels. Place another paper towel on top and press firmly to remove all additional liquid.
Separate spinach into easily consumable portions (I went with two 5 oz servings) and place into a Ziploc sandwich bag and place these bags into a one gallon Ziploc freezer bag and place into your freezer
As far as cost savings go I can buy chopped or leaf spinach for $1.49 for a 10 oz. package (same amount I made myself) This works out to $2.39 per pound, I can buy a 2.5 lb. bag for $3.00 ($1.20 per pound) or roughly half the price for a pretty simple process.