Objective The aim of this study was to explore Western Australian cancer patients' experiences of out-of-pocket expenses (OOPE) during diagnosis and cancer treatment using a phenomenological approach. Methods Semi-structured interviews were conducted with a purposive convenience sample of 40 Western Australian cancer patients diagnosed with breast, lung, prostate or colorectal cancer. Participants were asked about the impact of their diagnosis, the associated costs and their experience within the health system. Data were analysed using thematic content analysis. Results Three key themes influencing participant OOPE experiences were identified: (1) personal circumstances; (2) communication with health providers; and (3) coping strategies. Despite Australia's public healthcare system, several participants found the costs affected their financial security and resorted to coping strategies including medication rationing and restrictive household budgeting. The key themes had a complex and interrelated effect on patient OOPE experiences and were used to adapt Carrera et al.'s model of economic consequences of cancer treatment on the patient and patient coping to describe these relationships in a mixed healthcare system. Conclusion Organised efforts must be implemented to mitigate maladaptive coping strategies being used by cancer patients: (1) health providers should seek informed financial consent from patients before commencing treatment; and (2) financial aid and support schemes for cancer patients should be reviewed to ensure they are delivered equitably. What is known on this topic? The financial cost of cancer can have significant adverse effects on cancer patients. Although financial transparency is desired by cancer patients, its implementation in practice is not clear. What does this paper add? This study adapts a conceptual model for the economic consequences of a cancer diagnosis and repurposes it for a mixed public-private health system, providing a framework for understanding downstream consequences of cancer costs and highlighting opportunities for intervention. What are the implications for health practitioners? Health practitioners need to initiate discussions concerning treatment costs earlier with cancer patients. There are several resources and guides available to assist and facilitate financial transparency. Without urgent attention to the financial consequences of cancer treatment and related expenses, we continue to leave patients at risk of resorting to maladaptive coping strategies, such as medication rationing and restrictive household budgeting.