Sourcing rare earth elements (REEs) from unconventional feedstocks has substantial environmental and societal–economic benefits, but its economic viability remains unclear. Here we propose a framework for assessing the economic viability of unconventional REE feedstocks. We first develop a database of capital and operating expenses for REE recovery and establish consistent process unit costs for common stages in the conventional supply chain. We then use market prices to develop well-defined methods for determining diverse product values. Finally, we report the effects of economies of scale and feedstock purity on capital and operating costs. These tools can reduce uncertainty in the assessment of the economic viability of producing REEs from unconventional feedstocks, determine the value of innovative pathways for REE production from diverse sources and inform research priorities across a wide range of REE product development stages, contributing to a sustainable REE supply. Sourcing rare earth elements (REEs) from unconventional feedstocks has substantial environmental and societal–economic benefits. Here the authors develop tools to evaluate the economic viability of unconventional REE feedstocks to facilitate the implementation of a sustainable REE supply.