I don’t think “cost-benefit” is the best term to use because it immediately gets people thinking strictly in terms of finances.
I think the better word to use is product value because it combines financial aspects with other tangible and intangible benefits.
In other words, 15 years ago when the A shows were still for those showing at 3’ and above, there was an intangible value provided knowing you were skilled enough to be there and knowing that a ribbon won meant something. That value made it (more) worth the cost (which was considerably less than it is now).
Or in other disciplines, such as barrel racing, which offers many more prizes of various sorts, the value of the chance of winning those prizes makes the financial aspect more worth it. The western disciplines oftentimes have cars, trailers, trucks, saddles, buckles, etc. for prizes both at regular shows and as year-end or finals prizes.
Or in dressage, where one can qualify for regional finals with three scores at rated shows, the value of having a finals to work for and attend makes the cost worth it. Being able to say you qualified and went to regionals (even if you don’t place) is worth something. In the H/J world, the finals are all for the people who show the most, not those who ride the best.
Etc.
What we see in the H/J industry is the value of the product decrease while the price for the product increases.
This is an unsustainable trend for all but the wealthy who can afford to show regardless of the value or price.