You probably won't be surprised if I tell you that the price of a blockchain project varies a lot. Depending on what you are willing to achieve, the use of a certain infrastructure over another will range the investments from small to large. For example, the cost of authenticating official documents through a public blockchain will mostly comprise the transaction fees levied by the network to process the transactions, which is not a very expensive blockchain application. Using a public blockchain is sometimes the cheapest solution if we wish to benefit from an already existing infrastructure. Besides the transaction fees, the costs will mostly rely on developing the application on top of it and focusing on user experience.
On the other hand, if you are building an entire network from scratch, like Facebook is doing with their Libra Project...
