Speaking to ITV News Central at the Conservative Party Conference he said other transport projects will have more money spent on them than the planned high speed rail line HS2.
Sutton Coldfield MP Andrew Mitchell could return to the front line of the Government in future, David Cameron has hinted.
Mr Mitchell resigned from the Cabinet in October last year following allegations that he hurled abuse police officers outside Downing Street, calling them "plebs".
But an official investigation later uncovered CCTV footage which appeared to show the "plebgate" claims were wrong.
The Prime Minister, speaking ahead of the first day of the Tory party conference today, would not rule out a return to government for Mitchell.
He declined to talk about the incident as arrests have been made - but praised Mr Mitchell as a "very talented politician".
He added that he would wait until the investigation was over before making any announcements about Mr Mitchell's future.
"I have enormous respect for him. He was a brilliant (International) Development Secretary. I am very sorry about all the things that have taken place," he told the Andrew Marr show.
"We have to let this investigation take place and then we can take it from there."
Prime Minister David Cameron has promised that HS2 will not take up an "unfair share" of the government travel budget.
Speaking on the Andrew Marr show, he said the government would not spend "unlimited money" on the project and said they would be sticking to the £42.6billion limit.
He also explained his reasons for pursuing the plan.
This is the Government that delivered the Olympics on time and on budget. We are delivering Crossrail - the biggest construction project anywhere in Europe - on time and on budget. HS2 is going to happen.
The west coast main line is full. We have to build another one. The choice is do we build an old-style Victorian one or do we build one of the new high-speed lines?
I think people all over the country are worried that HS2 is going to take up too much money.
In the next Parliament, we will be spending more than three times as much on other transport projects as we will on HS2.
It's not taking up an unfair share of the budget.
Prime Minister David Cameron has today admitted there is a limit to the amount of money that he will spend on the HS2 rail link from London which will go through the Midlands to the North.
The future of the line linking the UK's major cities was thrown into doubt at last week's Labour conference where shadow chancellor Ed Balls said he would not provide "a blank cheque" for the project and would consider whether there were better options to use the £50bn of state spending.
But on the BBC's Andrew Marr Show, Mr. Cameron has insisted the project can be built within the Government's £42.6bn budget and rejected suggestions other more useful transport schemes were being crowded out.
The family of a woman from Coventry murdered in a so-called "honour killing" have written to the Prime Minister in the hope of getting the case reopened.
Surjit Athwal disappeared in India in 1998. Two people have been convicted in the UK of arranging her murder, but those who carried out the killing have never been caught. Peter Bearne reports.
Surjit's brother Jagdeesh Singh told ITV News he has written to Prime Minister David Cameron asking him to put pressure on the Indian Government to reinvestigate the murder of his sister Surjit Athwal.
Ms Athwal was killed in India in 1998. Her mother-in-law and husband were convicted of ordering the killing but no one has ever been found of actually carrying out the murder.
The brother of a woman from Coventry who was the victim of a so-called 'out sourced' killing in India has written to the Prime Minister to ask for him to intercede in the case.
Surjit Athwal was killed in India in 1998. Her mother-in-law and husband were convicted of ordering the killing but no one has ever been found who actually carried it out.
Surjit's brother Jagdeesh Singh wants the Prime Minister to put pressure on the Indian Government to further investigate the case and bring the issue to further prominence.
Her mother-in-law and husband claimed she shamed the family by having an affair.
Prime Minister, David Cameron, has tweeted following the news that Stiliyan Petrov has retired as Aston Villa Captain.
The Prime Minister has paid tribute to Sir Alex Ferguson - and suggested he could now help to make "life a little easier" for Aston Villa.
The Manchester United manager announced earlier today he is retiring, after 26 years in charge. David Cameron, who is a Villa fan, said Ferguson's contribution to football has been exceptional.