Step 1: Focus on the committee's job description.
We need the committee that specifically examines extravagance, that is, wasteful government spending, rather than one that audits money already spent.
Step 2: Recall the Estimates Committee's role.
It studies budget estimates in advance and suggests ways to bring about economy and efficiency in government spending.
Step 3: Eliminate the other committees.
The Public Accounts Committee examines spending after it has occurred based on the CAG's report, the Public Undertakings Committee reviews PSU performance, and Ad hoc Committees are formed for one-off specific purposes.
\[ \boxed{\text{Estimates Committee}} \]