The pricetag cannot be accurately predicted in terms of dollars, or any other currency. It will be what it will be and the money is available to purchase what resources and labor are necessary at any time. The question we need to be asking is "Do we have the ability to supply those resources and labor without completely disrupting our supply chains?"

We will have to stop considering taxation and borrowing as "revenue" and understand the reality of our monetary systems that only use them to control the money supply, never to "pay for" spending for the public purpose. Taxing $62 Trillion out of the global economy would drive most countries into famine and destitution, and it would serve no purpose in "funding" anything. Nevertheless, convincing politicians of every nation of this would be impossible and they would be reluctant to switch their economic worldview to a new reality, regardless of how correct that may be.

If we could ever achieve a global consensus agreeing to make the best effort possible the nations could simply give up the resources we need and only be paid for the labor used in the short term with promisary payment agreements for a longer term payout. This would, obviously, require a level of co-operation we've never achieved before.