Scott in NYC

Echoing Josh Martin, I don't think you'll find anything in Robert's Rules on this. It sounds like you're asking for the citation of a rule along the lines of "If there is money in a committee's budget, the procedure to spend it is X" or something like that -- but that's not the sort of guidance that RONR gives. If there is nothing clear in your by-laws or in the motion that formed the committee or allocated a budget, then check out how your organization spends funds in general. For example, if your organization needs to rent space for a membership meeting, what internal approvals are required to spend the money? Consider following the same approach.

If the motion had been well-thought out in advance, I'm sure it would have been structured that way. But it's not uncommon for a motion to be made without thinking through the budget. For example: "I move that we host a Membership Party on April 10 and invite Katy Perry to attend" -- that might get resounding approval. Then "I move that amend the budget to allocate $250,000 to pay for Katy Perry's appearance fee" -- that might fail. It's true that we lack information on this case, but I don't see it as far-fetched that a group might agree to something without agreeing to, or even thinking about, an exact cost.

Review your organization's by-laws carefully regarding spending money. If there is any guidance there, that may answer your question better than consulting Robert's Rules. It is common for organizations to spend money as approved in their budget without necessarily getting board approval for every expenditure. However, that is usually spelled out in the by-laws, and may include exceptions for ad-hoc purchases above a certain value. I hope this helps!