Private recruiting firms reaped a bonanza of more than $100 million in Commonwealth contracts in 2014, cashing in on the Abbott government's public service hiring freeze.

Spending by government departments on the big five recruiters soared by nearly 50 per cent last year to $97 million as public service bosses looked to temps and contractors to plug the growing gaps in their workforces caused by years of redundancies and the hiring freeze.

Spending by the Prime Minister's own department on workers supplied by the big five soared by more than 400 per cent, from $607,000 in 2013 to at least $2.6 million in 2014.

The federal opposition says the figures show the government's public sector policies are a false economy, allowing bureaucrats to leave with large redundancy payouts only to return, sometimes within weeks, as contractors.