The diet proposed by the EAT-Lancet Commission has faced criticism concerning its affordability. This study aimed to investigate the cost associated with a greater alignment to the EAT-Lancet reference diet in the province of Québec, Canada. The dietary habits of 1147 French-speaking adults were assessed using repeated Wed-based 24-hour recall data collected between 2015 and 2017 in the cross-sectional PRÉDicteurs Individuels, Sociaux et Environnementaux (PREDISE) study. Diet costs were calculated using a Nielsen food price database. Usual dietary intakes and diet costs were estimated using the National Cancer Institute’s multivariate Markov Chain Monte Carlo method. Adherence to the EAT-Lancet diet was assessed using the EAT-Lancet dietary index (EAT-I). Associations between diet costs and EAT-I scores were evaluated using linear regression models with restricted cubic splines. After adjustment for energy intake, a higher EAT-I score (75th vs. 25th percentiles) was associated with a 1.0 $CAD increase in daily diet costs (95%CI, 0.7 to 1.3). This increase in diet costs was mostly driven by the following component scores of the EAT-I (75th vs. 25th percentiles, higher scores reflecting greater adherence): Vegetables (1.6$CAD/day, 95%CI: 1.2, 2.1), Free sugars (1.6$CAD/day, 95%CI: 1.3, 1.9), Fish and plant-based proteins (1.4$CAD/day, 95%CI: 1.0, 1.8), Fruits (0.9$CAD/day, 95%CI: 0.4, 1.3), and Whole-grains (0.4$CAD/day, 95%CI: 0.0, 0.8). Inversely, greater scores for the Poultry and eggs component were associated with reduced diet costs (-1.2$CAD/day, 95%CI: -1.7, -0.7). This study suggests that adhering to the EAT-Lancet diet may be associated with an increase in diet costs in the province of Québec.