Plasma p-tau217 may offer a cost-saving effect in diagnosing Alzheimer’s disease. However, each healthcare system has different costs, and its impact on evaluating anti-amyloid β (Aβ) therapies in Japan remains unclear. We conducted cost analyses using a two-step approach with a recently released application, assuming that measuring two analytes (p-tau217/Aβ42) would reduce the intermediate zone to 7%, despite doubling the price. Plasma biomarker costs were simulated from 100 to 800 USD. Cost savings ranged 34–79% compared with positron electron tomography (PET) and -5.6%–74% compared with in-patient cerebrospinal fluid (CSF) Aβ42/40 when 14.7% were in the intermediate zone. Savings were comparably high by measuring two analytes at 100 or 200 USD per analyte and gradually differed (one analyte better savings than two) as the cost per analyte increased. Both plasma p-tau217 and p-tau217/Aβ42 showed substantial cost-saving effects, with comparably high savings at lower costs (100, 200 USD) per analyte.