It's been my experience that most business needs involving estimates can't wait until the job is partway done. "Can we afford this" and "should we do this now" really need some up front answers :)

Vistimo Quotes is specifically for producing rapid estimates that don't require team buy-in, sign-up, etc.

Vistimo (https://www.vistimo.com) does anonymous, asynchronous team estimation -- but the additional labor costs (sufficiently describing tasks to async folk understand them, managing team permissions, requesting reestimate when requirements change) have made it not particularly viable as a product.

Finding a balance of power and simplicity is never easy.