Charities are being offered cut-price airtime as demand for TV adverts falls in the recession.
The NSPCC, Dogs Trust, WaterAid and Action for Children said they had benefited from lower rates as channels looked to fill their advertising quotas.
A spokeswoman for the NSPCC said the cost of the charity's TV advertising was about 25 per cent lower than it was a year ago.
WaterAid said Channel 4, whose costs are normally too high for the charity's advertising budget, had offered cheap airtime. A spokeswoman for the charity said this was because of falling demand from major advertisers such as car manufacturers and banks.
Kerry Glover, head of donor recruitment at Dogs Trust, said: "We're getting more for our money without having to increase our advertising budget."
Andy Preston, managing director of Outstanding Result, which advises charities on negotiation work, said many charities could miss out. "These bargains are often last-minute," he said. "Charities should send ads to sales firms speculatively; they'll use them when they can't sell their space."