The "Transit Bus Affordability Act" mandates that the Comptroller General of the United States undertake a comprehensive review of the factors contributing to the high and rising costs of transit bus manufacturing and procurement in the U.S. The central goal is to recommend strategies for mitigating these expenses and ensuring the efficient use of Federal, State, and local funds in acquiring new buses for public transit. The review will delve into the primary cost drivers in the design and procurement process, comparing U.S. costs with those in other countries and analyzing price increases over the last decade against other commercial vehicles. It will also assess the effects of manufacturing and supplier challenges on Federal Transit Administration-funded procurements, such as those under the low or no emission grant program. Additionally, the Comptroller General must evaluate steps taken by various stakeholders to reduce bus costs and accelerate delivery times, including the impact of joint procurement and any necessary additional authorities. A detailed report outlining these findings and recommendations is required to be submitted to the House and Senate committees responsible for transportation within 18 months of the bill's enactment.