Expect roughly $250–$600 for many mainstream under-sink RO systems and $300–$900 for countertop or premium appliance-style systems. Annual filter cost can matter more than the initial price over several years.
Traditional tank RO
Standard tank-based systems are usually the least expensive architecture and often use standardized filters, which can reduce long-term parts cost.
Tankless RO
Tankless systems typically cost more because they include higher-capacity membranes, pumps and electronics. Frizzlife PD600 is a current example around the high-$300 range before promotions change.
Premium countertop RO
Countertop systems add feed tanks, displays and sometimes hot/cold dispensing. RKIN U1 currently sits around $875, illustrating how feature-rich countertop RO reaches a different price tier.
Replacement cost
Model-specific cartridges are the long-term cost center. Compare annualized cartridge cost before deciding that one system is cheaper.