Tasmanian Greens Senator Peter Whish-Wilson said the proposal would replace an existing scheme that compensated exporters.

He said the proposal would need to operate for 20 to 30 years, but could potentially be self-funding.

"The Bass Strait freight equalisation scheme cost taxpayers over $100 million last year alone. If this continues we will clock up a bill of more than $1 billion in freight subsidies during the next decade," Senator Whish-Wilson said.

"Everyone seems to just focus on throwing more taxpayer money at the problem, but what the Greens will be exploring is sustainable long-term infrastructure financing and development options."

Denison independent MHR Andrew Wilkie has already announced he wants the major parties to expand the existing freight scheme and estimated that will cost another $60 million a year.

"That is the view of exporters I've spoken to, but of course the final figure can only be determined by government in consultation with industry," Mr Wilkie said yesterday.

The Coalition has promised a review of the scheme.

Meanwhile, the federal government has provided $20 million to the state to compensate exporters paying more to ship goods since a direct international service was lost in 2011.

The Tasmanian government has set up a taskforce to investigate that issue, and the state opposition has promised to spend $33 million over three years to attract an international shipping service back to the state.