A project is defined as a level of effort with a defined BEGINNING & END.
Estimated costs regarding HW, SW, RESOURCES (internal & external), 3RD party contracts, etc. are dependent on understanding the LOE supporting those task / deliverables. There would be no way to come in "on-time" & "on-budget" without something to measure yourself against. Additionally, skilled resource availability is based on knowing when they are needed to execute their set of tasks. The project NOT having a defined completion date will interfere with any resource being comfortable in committing to participating on the project.
This being said, "YOU", as the PM, have the opportunity to create your own target based on the understanding of the scope of your project. You have "XX" BUDGET to execute "YY" tasks. Internal commitments can be made based on those estimates giving those needing to know "when" the project is estimated at being completed.
Bottom line, if there is NO WAY to define the "end of the project", work shouldn't begin. Saving Changes...
"People are always blaming their circumstances for what they are. I don't believe in circumstances. The people who get on in the world are the people who get up and look for the circumstances they want and, if they can't find them, make them."
