The Abbott government has floated the idea of combining the cap on the annual amount that pensioners and concession card holders have to pay for visits to the doctor and for medicines as it begins detailed budget negotiations with the Senate crossbench.

The budget proposed to increase the pharmaceutical co-payment for concessional patients by 80 cents to $6.90, with the upper limit on the number of scripts for which they have to pay that amount increasing from 60 ($366 a year) to 62 in 2015 ($427.80 a year) and 68 in 2018 ($469 a year).

It also proposed the introduction of a $7 co-payment for visits to the doctor, with concession card holders and children under 16 required to pay for their first 10 visits, a maximum of $70 a year.

As federal cabinet met to discuss the apparently stalled budget, crossbench senators told Guardian Australia the government has floated the idea of a single cap on out-of-pocket payments for both visits to the doctor and medicines, in line with the current cap on the Pharmaceutical Benefits Scheme (PBS).

The Liberal Democrat senator, David Leyonhjelm, confirmed it was an idea that had been raised by the government in talks. The Family First senator, Bob Day, met the health minister, Peter Dutton, on Monday morning and said it had been part of the government’s “opening gambit”.

The changes to the PBS co-payment are scheduled for debate in the Senate this week. Labor has said it will vote against both the Medicare and PBS changes, releasing figures over the weekend about the combined effect on household incomes per electorate, based on previous statistics about visits to the doctor and PBS use.

The idea of a combined safety net has been publicly backed by Tony Abbott’s former policy adviser Terry Barnes, now a health policy consultant who began the debate on the GP co-payment idea last year.

Barnes told Guardian Australia last week the co-payment debate had highlighted the need to reform safety net arrangements for both the PBS and the Medicare Benefits Schedule (MBS) and said it did not make sense for policy to consider the two issues separately.

“In the interests of fairness and transparency Medicare and the pharmaceutical safety nets should be combined so we look at people’s total health spend not just bits of it,” Barnes said.

“It’s become very clear to me over the last few months you can’t look at a person’s Medicare spend without looking at their PBS spend.”

The Greens and the Palmer United party have ruled out support for the GP co-payment.

PUP’s Senate leader, Glenn Lazarus, was asked on Brisbane radio 4BC on Monday whether PUP would vote for the GP co-payment in any form.

“No, we won’t,” Lazarus said. “At the end of the day it adds up and I just don’t think we are in a time when we need to be paying to see the doctor.”

Day said he had advised Dutton to “pull right back, take things slowly and start with very low co-payments”.

He said the fact the co-payment revenue was slated for the new medical research future fund was “muddying the government’s budget message”.

Dutton has said he is “hopeful that the government can do a deal in relation to the GP co-payment because there is certainly a lot of optimism from the senators. That’s my assessment and I believe that they, like the government, want to have a Medicare that is sustainable for the next generation. I’ve found our meetings to have been quite productive so far and they’re early days, these are long-run negotiations.”

Dutton said recently a blanket exemption for anyone on a pension or under the age of 16 would represent “almost 9 million Australians out of a population of 23 million” and an Australian Medical Association (AMA) plan, which included exemptions for both groups, would wipe out 97% of the government’s proposed savings.

Labor’s leader, Bill Shorten, repeated his party’s opposition on Monday, saying: “I can be very clear and send the message through you – the GP tax is a tax on the sick. We’re not voting for it. Australians already pay for their healthcare through their Medicare. We’re not into making it harder for people who need healthcare to get it.”