This is a skill that needs to be learned from working in a particular industry. A lot of the time someone inexperienced won't know the total cost until they get their final quotes from their supply chain. Even then maybe some don't even realize until after they have paid.
For consumer electronics, the average markup needs to be at least 4 times the COG (cost of goods) which is what you spent to make the product, usually in bulk, in order to make a 50% profit. And that is if you do a lot of work yourself. The more logistic help you require the more the factor increases. I am sure it is similar in other industries.
"Will someone buy this for what it costs to make" should be the very first research goal, followed by "make it and see if it even works", and then "please convince me that no one will buy this" when you show it to friends/test group. I don't think the bitman rack followed these steps.