I have just 2 75 cent coupons right now, not worth the price to mail, but at our grocery store there is a store brand sold also, that is about $2 cheaper. So it would be cheaper even with a Pediasure coupon, the highest coupon I have seen in about 1 year of using a nutrition drink is $1 off.
Other ideas- my youngest is failure to thrive, low weight, here are some things from her feeding clinic-
Carnation Instant Breakfast highly recommended. High calorie, high protein- add cheese to everything. Add peanut butter, Add margerine or corn oil to hot foods like soups and vegetables, mashed potatoes, cooked rice, pasta. (We add extra butter to her mac and cheese, and her scrambled egg has extra butter.) Add chopped hard cooked egg to salads, and extra egg to pancakes, French toast. Serve foods that are breaded and fried. Use mayo at 100 calories a Tbs over salad dressing at 50 calories a Tbs. Add granola to baked goods. Instead of water, drink fruit juice, yogurt drinks, eggnog. Make shakes with Carnation Instant Breakfast, whole milk, and ice cream. Dip raw veggies in salad dressing, yogurt dips, sour cream. Dip fruit in marshmellow creme or cream cheese. Use whipping cream or half and half in puddings, on cereal, in cocoa. Have crackers with cheese, butter, peanut butter, frosting. Add powdered milk to anything you can.
Hope some of these can help, it is nice to have the complete meal in the Pediasure, but look for ways to add calories, fats, proteins every meal and for two snacks a day.