Background: Despite the recognized side effect of financial toxicity after cancer, treatment decisions for breast cancer rarely include the costs of care. We sought to determine women’s experiences with breast cancer treatment costs, and their preferences for cost transparency at diagnosis. Methods: Women ≥18 years old with a history of breast cancer completed an 88-question electronic survey based on validated or published items. Descriptive statistics and regression analysis were used. Results: In total, 607 women with stage 0-III breast cancer participated. Median age at diagnosis was 49.6 years. Median time from diagnosis was 6.7 years (range 0.1-37.1). The majority had private (70%) insurance or Medicare (25%), and reported an annual household income ≥$74,000. 43% reported considering costs in treatment decisions. Median reported out-of-pocket (OOP) costs were $3,500; 25% reported OOP costs ≥$8,000, 10% reported OOP costs ≥$18,000 and 5% reported OOP costs ≥$30,000. 15.5% reported significant to catastrophic financial burden. Bilateral mastectomy +/- reconstruction vs lumpectomy (OR 1.9, p 0.03), greater stage at diagnosis (stage 3 vs 0, OR 3.9, p < 0.01), and discussion of costs during the clinical encounter (OR 2.3, p < 0.01) were associated with a higher risk of financial harm. Women who reported discussing costs were more likely to be stage 2 or 3 (56% vs 40%, p = 0.02), less likely to be depressed (24% vs 30%, p = 0.03), and had less insurance coverage (trend p = 0.02) compared to those who did not. Older age (OR 0.95, p < 0.01), increasing household income (overall p < 0.001), better insurance coverage (OR 0.5, p < 0.001), and longer time since diagnosis (OR 0.65, p < 0.001) was associated with a decreased risk of financial harm. 78% of participants never discussed costs with their cancer team. 79% preferred cost transparency prior to embarking on care, and 40% preferred that doctors consider costs when making recommendations. Conclusions: Many women with breast cancer reported significant financial burden related to their care, and the vast majority preferred knowing costs at diagnosis. Cost transparency may improve the quality of preference-sensitive treatment decisions and reduce the risk of financial harm.