It is understood Mansell has been offered around $7m (£4.4m) for a one-year contract with McLaren-Mercedes, but that he is seeking nearer $1m (£640,000) for each of the 16 races in the World Championship.
The 41-year-old Englishman made four appearances for Williams-Renault at that rate last season, yet was rejected by the Didcot-based team in favour of David Coulthard.
McLaren appear to represent Mansell's last option in Grand Prix racing, and Ecclestone warned that unless he moderates his demands his career at this level could be over.
Ecclestone said: "He'd be stupid if he didn't go to McLaren. If he doesn't go there he won't go anywhere. The stumbling block is money. He probably thinks he's worth more than he is really.
"The chances of Nigel driving for McLaren, I would hope, are higher than 50-50, but whether it is 50-50 or 90-10 it's the same. It ain't happened yet."
Ecclestone, keen to add Mansell's box-office appeal to this season's championship bill, added: "Nigel is talented and a very useful person in Formula One. He will motivate any team he is going to drive for.
"But there is a limit to what people are prepared to pay for him and his abilities. He's asking enough to make it not viable."
There is a commonly-held belief that Ron Dennis, the managing director of McLaren, would be reluctant to take on a driver he has never pretended to like, but Ecclestone is adamant that is not an issue. He said: "If they get things together it will be forcommercial reasons, not for any other reasons."
Dennis could take on Jacques Villeneuve, the Canadian driver who has made a big impression in IndyCars, for $2m, or retain Martin Brundle for probably less still.
Commercial reasons were behind the demise of Lotus earlier this week, though Ecclestone suggests they were pushed before they could jump. FIA, the governing body, was unwilling to accept their entry because it was felt the team would not be in a positionto fulfill their commitments for the season. It also seems highly unlikely the Lotus name will be revived elsewhere or at any stage in the future.Reuse content