It is widely anticipated that Level-4⁴ (L4) autonomous vehicles - vehicles capable of autonomously performing all driving functions under certain conditions - will eventually become available to the public. However, these vehicles are likely to be expensive due to the additional requirements on hardware, making them potentially inaccessible to the average consumer. This paper introduces the concept of Affordable Autonomy through Cooperative Sensing and Planning (AACSP). This concept enables a vehicle equipped with lower-end sensors such as a Level-2⁶ vehicle - vehicle capable of limited lateral and longitudinal control but requiring a driver to stay engaged - to enter into an autonomous mode whenever it is in proximity with a Level-4 vehicle traveling along the same route. The paper describes the system along with the technical components of cooperative planning & state coordination in detail while giving an overview of the cooperative perception and localization modules that are required to implement the AACSP concept. The paper also presents results from simulation and real vehicles.