How do economic costs affect religious group membership, and how do religious organizations respond to exogenous changes in membership costs? We study these questions in the context of the Seventh-Day Adventist (SDA) church in Sub-Saharan Africa. The SDA church prohibits or strongly discourages tobacco, coffee, and tea production, leading opportunity costs of membership to vary based on local crop suitability and global prices. We construct a measure of SDA membership opportunity cost that varies over time and space. Using detailed church data alongside SDA member surveys, we analyze responses by both members and the church itself. We find that increased opportunity cost of membership leads to fewer new memberships, and more self-reports of struggle and doubt about spiritual beliefs among current members. In turn, the church pursues offsetting responses, establishing educational institutions (generating new benefits of membership) and potentially reducing emphasis on some religious tenets (reducing the costs of membership). This study provides new insights that individuals and religious organizations actively respond to economic incentives in the religious marketplace.