There does not appear to be a precise, universally agreed-upon figure yet for how much AIPAC itself spent specifically to defeat Thomas Massie in the 2026 Republican primary, but multiple major outlets report that:

The race became the most expensive House primary in U.S. history, with total spending estimated between $25.6 million and $32+ million.
A substantial portion of that spending came from pro-Israel groups and donors aligned with or associated with AIPAC.
Massie himself publicly claimed the Republican Jewish Coalition alone spent about $3 million against him.
Reporting from Reuters and other outlets described “significant spending from pro-Israel groups” but did not isolate a final AIPAC-only number.