With the new two-step process of applying in Grants.gov and then later in JustGrants, I am unsure how to deal with the budget. Does my budget need to be complete before the first deadline in Grants.gov?

Once you get into JustGrants, you can update most data fields associated with the SF-424 (e.g., requested funding amount, project title, type of applicant). The only data that cannot be edited directly in the application are the entity identifiers (e.g., DUNS).  Therefore, it is okay to put a “placeholder” budget amount to meet the Grants.gov deadline and change it later.