The Scottish Government has provided a funding package of £16 million to cover the costs.
HIE said it had diverted unallocated funds from its wider capital investment package for the Cairngorm Snow Sports Center Masterplan to cover the additional costs.
The agency added that the Scottish Government had also committed £7m of additional funding in June 2022.
Opened in 2001 at a cost of £26 million, the funicular links a base station with a restaurant and ski area 1,097 meters (3,599 ft) up the Cairn Gorm mountain near Aviemore.
Renovation of the rail track started in April 2021.
Testing of the funicular is expected to continue in December and safety certificates will be required from the UK Department for Transport before it can be opened to visitors.
There has been criticism of efforts to restore the railway.
Last year, mountaineer and writer Cameron McNeish, who opposed plans for the funicular before it opened in 2001, said the railway should be “removed” from the mountainside and the area returned to the wild.
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