The Scottish party leader said taxes will have to rise or services will be cut to maintain popular but expensive SNP pledges on areas such as the council-tax freeze.
First Minister Alex Salmond is passing the buck to already stretched local governments, she said in a speech in Edinburgh.
"Scotland cannot be the only something for nothing country in the world," she said.
Underlining the rapidly-expanding number of older people and the squeeze on finances, she added: "This is the stark choice that Scotland has to face up to: if we wish to continue some policies as they are then they come with a cost which has to be paid for either through increased taxation, direct charges or cuts elsewhere.
"If we do not confront these hard decisions soon, then the choice will be taken from us when we will be left with little options."
A group will be set up by Labour to look at the economy and a university professor will help provide fully-costed policies, she said.
"I pledge this to the people of Scotland," she added.
"What I will say will not always please you, but what I say will always be honest and true and how I genuinely see it.
"I will not promise what I cannot deliver. And I will never hide the cost of what I propose."
Ms Lamont, speaking at the Hub venue near Edinburgh Castle, referred to work already undertaken on the delivery of public services in Scotland at a time of austerity.
The Christie Commission warned of difficult spending decisions and Lord Sutherland - the architect of free personal care for the elderly - indicated that cuts are inevitable unless taxes fill the gap.
As well as putting a question mark on the council tax freeze, Labour may also consider tuition fees for students and an end to universal NHS prescriptions.
The party said no decisions have been taken but all areas will be looked at, including centrally-imposed targets.
One benefit the party said was unlikely to be significantly changed is bus passes.
Interim reports should be expected in one to two years but there will be no manifesto before the proposed referendum on independence, expected to be held in 2014.
Ms Lamont said she is "calling time" on what she called a dishonest auction among political parties.
"I know that there are families, working hard, on average or above average incomes who feel they pay enough and are attracted by policies like free prescriptions, free tuition fees and the council-tax freeze," she said.
"I know where they are coming from but I ask them to look at how they are paying for those free things.
"What price your free prescription when an elderly relative spends five hours on a trolley in A&E or the life-saving drug they need isn't available at all?
"What price free tuition fees when your neighbour can't get a place at college or when university standards are now lower than when they went to uni?
"What price the council-tax freeze, when your parents' care is cut, and your child's teachers cannot give them the materials they need because there is a ban on something as simple as photocopying?"
The SNP focused on slogans rather than policies, she said, while "underfunding" expensive pledges.
"The constitutional debate which we have had now for more than half a century - be it about devolution or independence - has meant that when we say change in this country, the only thing we mean is constitutional change," she continued.
"But we can change Scotland now. We have the powers in the Scottish Parliament now, to change radically education, health, public services. What we lack is the will.
"What we lack, and what is crowded out by the referendum debate, is a real debate of radical ideas about how we change Scotland now.
"We need to break out of the straight jacket of saying that more powers to politicians alone is the way we change the country.
"We need people's attitudes to change. We need individuals and communities to feel empowered to change their lives.
"Yes, we will change devolution but we need more profound change than even that."
Ms Lamont criticised Finance Secretary John Swinney as "George Osborne in a kilt".
"Some might even argue that John Swinney thinks it is in his political interests not to protect Scotland from the Tory cuts, but to let them run free in the hope that the pain they cause ordinary Scots will help him in the referendum," she said.
"I am not going to get into an auction with the SNP. They might cry freedom but the idea that Scotland is a land where everything is free is a lie. Someone always pays for it in the end."
Nicola Sturgeon, the SNP deputy leader and Deputy First Minister, said Ms Lamont is embarking on a disastrous approach.
"Almost one year on from her election as leader and Labour still have no policies of their own to bring to the table," Ms Sturgeon said.
"Establishing a commission for cuts but hiding the final conclusions until after the referendum is simply pushing Labour's policy problems into the long grass."
The SNP is protecting households from the impact of UK Government spending plans, Ms Sturgeon said.
"At a time when people are facing serious wage restraint and rising living costs, the council-tax freeze, the abolition of charges for prescriptions, support for higher education, apprenticeships and the elderly are all part of the support we in society give to each other," she added.
"To destroy those shared social bonds, that we all pay for through our taxes, is a disastrous approach for Labour and one that will only increase support for an independent Scotland.
"All Johann Lamont has achieved with this morning's hastily-arranged press conference is to highlight the successes of the SNP in Government.
"If Johann Lamont thinks that mimicking the Tories on police, prescriptions and tuition fees is the way ahead, she really has lost touch with the people of Scotland."
