Reprioritizing Unserved Rural Areas and Locations for Broadband Act of 2018 or the RURAL Broadband Act of 2018 This bill amends the Rural Electrification Act of 1936 to allow financial assistance provided by the Rural Utilities Service for the deployment of broadband-capable infrastructure by a service provider to be used to provide retail fixed broadband service in an area where there is no qualifying broadband-capable infrastructure owned or operated by another service provider. The term "qualifying broadband-capable infrastructure" means fixed broadband-capable infrastructure: (1) used by a service provider to provide fixed broadband service for which the provider receives universal service support funds, and (2) was financed with funds from the Department of Agriculture.