Replacing part of the Laxey to Ramsey electric railway with a cycle lane would cost £8 million, according to the Department of Infrastructure.
A Freedom of Information request asked for documents about replacing railways with paths for walkers or cyclists.
In its response, the DOI released internal notes about the cost of making a 10-mile stretch of the MER single-lane for trams and installing a path.
The document says a path would cost £2.7 million, fencing £1.8 million, signalling another £2 million, and £400,000 each for track removal and drainage.
It also says the project could bring 'negative publicity', and hasn't been approved.