Trying to find a source for low cost or no cost Boost High Protein supplement drinks.

Forgot to say there are now generics which are a little cheaper. Walmart has Equate.

If you have a feeding tube (approved by Medicare) you will also be given the formula delivered once a month per prescribed amount. The very high protein may give the patient diarrhea.

I know responding to fossil posts is weird. But others might also stumble on here looking for similar solutions.
Ready-made formulas can be found at most drugstores, grocery stores, Walmart's, Costco's, etc. Even more can be found at health food stores or Co-Op grocers, as powders and ready-to-drink single-servings.
The real question is: what is the nutritional focus of the formula you buy?
Does your elder just need calories? More protein? Don't care about nutritional value it has? Don't care that sugar or artificial ingredients might increase Alzheimer's symptoms? Or does your person need more nutritional value?
There are many ways to MAKE a taylor-made formula at home, using fairly easy-to-get ingredients. Some off-shelf basic powders that mix with water, etc., others, need more separate ingredients.
I've tried MANY ready-made powders; most are junk; I look for ones that have best nutritional profile, then go from there.
I've made some that start with a base of plain or vanilla soy milk [Costco], which I add 1/2 pod of concentrated "Goodbelly" probiotics to one liter of soy milk, then allow to ferment overnight in the refrigerator.
To 1 cup of Goodbelly fermented soy milk, add: 2 heaping tsp. Nutritional yeast [local CoOp grocer or online], 1 to 2 scoop Amazing Greens powder [Costco, 45 servings I think], and a scooper of mineral powder. If I want to sweeten it, can add some of 100% fruit juice, or a small amount of stevia, monk fruit, or other.
I've also used 1 c. Goodbelly fermented soy milk + 1 or 2 raw organic free range eggs, vanilla, coconut sugar or honey, cinnamon, nutmeg, etc. spices, mineral powder and 1 Tblsp. flax seeds, 2 tsp. nutritional yeast, and a dollop of MCT oil... blenderized, to make an eggnog-like nutritious drink. The flax seeds give good fats and nutrients too, plus they thicken the liquid. Most elders I've worked with [and family members], think it's a treat...really, they are getting good nutrition.
If someone needs to gain a bit of weight, boost the MCT oil, and/or add another egg. and perhaps add some protein powder.
These are quick, easy, and tasty enough that people drink them; they are also diabetic safe...for those, I take more care to use stevia and monk fruit, and make sure the minerals are in it, since those help the body use carbs, and, help the tastebuds taste. Everyone's tastebuds differ though, so you might want to play with recipes a bit to find the right amounts of ingredients for you.
We keep chia and flax seeds in the fridge; never grind them until just before use.
We try to keep nutritional yeast on hand all the time, since it's cheaper than buying good B-Vit. supplements, and doesn't require pill-swallowing.
We also keep a good mineral supplement powder on hand, such as Mt. Capra Mineral Whey, or Mezotrace mineral powder.
Also, usually have some good-quality protein powder on hand, such as Mt. Capra's, or Terra's whey, in case anyone needs more protein.
NOTES:
Soy has a component that blocks absorption of certain nutrients. That is why it's important to ferment it using good probiotics.
I found the 4-pack GoodBelly probiotics pods at our local CoOp grocery: one pod will ferment two liter boxes of the Costco Soymilk; it keeps in the fridge for several days...it might get a bit thicker, but it's good.
The other easy/tasty probiotics are in commercially made Kombucha. For some months, Costco has carried a 6-pack of ginger Kombucha. But also found our Grocery Outlet often has many flavors of Kombucha, Kefir, etc., which we take advantage of...their prices almost match Costco's, whereas the CoOp kombucha can cost at least $1+more per bottle. Berry flavors are great; Cinnamon flavor is interesting. All taste refreshingly fizzy, and a great alternative to sodapop or empty calorie sugary drinks, as long as your elder can tolerate that [no swallowing problems]. It will "go flat" if left open a little...just like sodapop, the fix depletes if container allows it to escape.
One big reason for using probiotics: Nothing so far, has been able to completely stop progress of Alzheimer's. But new things DO come up....and MIGHT be helpful. This article just landed in my in-box: https://www.sciencedaily.com/releases/2016/11/161110162840.htm
It's a study about using [_broad-spectrum_] probiotics supplement daily, to help decrease the severity of Alzheimer's.
At least one strain of good bacteria can also help reduce depression and anxiety [L. Rhamnosus]
IDK if probiotics also help other Dementias, _but it very well might_, since gut health is what every other system depends on.

My Father in Law got his thru Home Health care . He was drinking Ensure but has a feeding line so they changed him to a formula product Medicare covers.

Ooooh - adding the powder to a pudding mix is a wonderful suggestion to bump up the flavor! Didn't think of that one!!! My mom doesn't care for chocolate (therefore she can't possibly be my mother...haha!) & the vanilla gets boring after awhile when it's too cold for a shake with fruit added. Any other suggestions??? Thanks!!

You can make a more flavorful concoction than anything in a bottle or can. There are many excellent whey-based (skip the soy) protein powders on the market. If weight loss is an issue, you can also increase calories with additives such as peanut butter or coconut milk instead of milk. As a family, we start our day with home made protein shakes mixed in the blender. You can find quite a few recipes online as well, to keep things interesting. For example, cocoa powder, peanut butter, and butterscotch pudding mix (sugar free or regular) renders a wonderful Butterfinger milkshake flavor.

If you know anyone who has a Costco membership, you can get a BIG bag of Muscle Milk powder - I'm not sure of the weight, but it's at least 3-5 pounds - for around 30 bucks. It has less sugar, less carbs, less fat, but almost double the protein of Boost (important if your loved one is diabetic, as my mother is). It's available in vanilla or chocolate there.

Boost High Protein ( 14 grams) can be found at any good supermarket. The cost is $7.00. This powder form can be mixed with either 2% fat milk or fat-free milk.

Go to Sams Club, Costcos or some other wholesale club, it is where I get mine for my mother. You can buy them in bulk and they are some cheaper. I do not think you will get them cheaper than that and they definately not free, I have bought them for 15 years. When I am out I use Carnation Instant Breakfast. You can get that in big cans. It is about the same thing only not reconsituted.