Leucine. Isoleucine, valine, glutamine and Airginine are NOT CHEAP. I would say the majority of cheap amino usually used is Glycine and Taurine.

Just look at Muscletech's Mass gainer and protein. You'll see the openly list Glycine above 1000mg. Glycine is naturally occurring amino acid but should not go above 500mg.

Taurine and Creatine totally has no business in protein and weight gainers with protein.

Beware of so call Post Workout Protein with Creatine or Mass Gainer with Creatine.

Simply look at the Ingredient list.

Glutamine/Taurine and Creatine are NOT BAD. It's just that they have their own place in supplements. More like stand alone.

Taurine is extremely important to avoid muscle cramps. You need around 2000mg per serving before any sporting event or rigorous [physical activity like hiking and mount climbing. Those who use Clenbuterol hcl use Tauring to avoid cramps. Taurine should be in any post-workot drinks.

Creatine is best taken by it self, not into any blend or formula. Use creatine with CREAPURE logo on it. Creatine will only work if your body is in fasting state like - upon waking up and after a workout.

Glutamine is great if you want to prevent or cure your gastric. Yes it meant for gastric patients. All research on Glutamine done are for gastric related to physical and mental stress. However real world results has proven that it helps maintain muscle and improve definition - if taken 60,000mg a day/60g (10g x 6 times). Not 5g a day that supplement companies recommends and want you to believe.
Using creatine in Mass Gainer is one way to reduce protein raw material cost and spike protein so it can pass the lab test. Remember Gainer formula is 80%Maltodextrin and 20% Protein. The 20% protein is just one way to window dress their product. In actual there is very less actual protein used.

Any good protein should has at least 64% protein content to 74%. There is no such thing as 100% protein because the protein grade is 80%, 20% is others such as moisture, ash, lactose, and etc. Highest protein in 30g serving powder should be 23g max. More than that you should beware.

Also, when buying gainer, make sure these ingredients are not there - creatine, taurine, glutamine, sunflower oils, corn syrup, glucose polymers, non-dairy creamers.

A good gainer should only contain these ingredients:

Maltodextrin (not glucose polymers, no oats or waxy maize shit)
Protein Blend or any single protein.
Cocoa (for choc only), other flavours contains colourings and food dye known as FD&C
Flavour
Soy lecithin as emulsifier
Sweetener (Acesulfame, Sucralose or stevia).
silicone dioxide or anti-caking agent (optional)
ADDed vitamins known as Premix does not take much space in each serving size.

Hope this helps.