Public Health/efficacy testing
If I have a product (dietary supplement) to be released in the US whose efficacy I hope to scientifically prove and document beyond anecdotes, perhaps on a test group of 150 people (50 per group: control, placebo, product). How much do you think a study like this would typically cost?
Also, does the paper on that have to be published in a scientific journal to be considered legitimate, or we can cite this to our customers as is (aka self-published/self-promoted)?
The only valid conclusion from a study this small might be something like: "More studies are needed." From a business standpoint I don't see how what you've suggested can be cost effective. Consider sticking with anecdotal or testimonial results and publish them as such.
Most consumers don't know the difference between what is scientific and what isn't. That's why products that talk about "results" are useful. (The conclusions drawn are either not statistically valid or aren't repeatable).
The idea that a dietary supplement can improve health beyond what is found in a healthy population is an oxymoron because a supplement isn't a drug or enhancement. For a dietary supplement to be valuable those who use it need to be deficient and the deficiency is replaced by the supplement. But excess nutrients just make expensive urine.
A scientifically-based conclusion is one based on supporting statistics. The statistics are gathered from a study that seeks to prove the opposite is true (the null hypothesis) and the study results must support rejecting the null. The approach proposed won't accomplish this.