The National Trust for Scotland has launched an appeal to find 1,000 donors willing to give £500 each towards the new Culloden Battlefield centre.
An artist's impression of the new centre
The trust said the need to raise £500,000 before 5 May is "urgent" to make up a funding shortfall.
Plans for the building must be finalised by that date if it is to be completed in time for the 2007 Highland Year of Culture.
Letters have been sent to trust members from new chairwoman Shonaig Macpherson.
Life and culture
The new building will replace the existing one which the trust said attracts more than 250,000 visitors a year.
Culloden Moor was the scene of the last major battle fought on mainland Britain.
The battle that took place on 16 April 1746 and effectively ended Jacobite hopes of restoring the exiled Stuart dynasty to the throne of Britain.
The army of Prince Charles Edward Stuart was crushed by government forces led by the Duke of Cumberland in less than an hour.
The brutal measures imposed after the battle signalled the end of the distinctive way of life and culture of the Highland people of Scotland.
The new centre will be built on the site of the existing one
In her letter, Ms Macpherson said: "Before I share with you our vision for the site, I must first emphasise the urgent need to raise the £500,000 to ensure the project lives up to expectations ready for the Year of Highland Culture next year.
"A fantastic £6.05m has thankfully already been raised.
"Now I need you to join me and lend your support to what is essentially the most significant project ever undertaken by the trust."
She added: "Plans must be finalised by Friday 5 May.
"Time is running out. I sincerely hope I can rely on you to help fund this incredible project - the story must be told."
Trust members who have received the letter are told the money could help pay for new technology to help bring the moor's "history alive" and aid in the restoration of the battlefield.