The average upfront cost of a 15-minute consultation with a GP could exceed $100 within two years under the federal government's proposed changes to Medicare, the Doctors Reform Society says.

The society, a lobby group that supports publicly funded universal health care, says the Abbott government's plan to reduce the Medicare rebate for doctors by $5 and freeze it until 2018 is promoting a "return to a failed privatised system of the past" with doctors free to charge what the market will bear.

Out of pocket: Dr Ralph Audehm at Dianella Community Health in Broadmeadows, Melbourne. He is likely to start charging his patients at least $5. Credit:Eddie Jim

Society national president and GP Con Costa said extending the current two-year-long freeze on Medicare rebates for another four years would hit GP clinics' budgets hard, driving many doctors away from bulk-billing and into increasing their fees for patients who do not have concession cards.

One GP said the changes would be devastating for the working poor and might stop them from seeking medical help.