The loo on Handa, off Sutherland's north west coast, was so expensive because it has to withstand gale-force winds and be environmentally-friendly.
This year, more than 7,000 people visited the isle which is home to more than 100,000 seabirds.
The toilet has been fixed so that it can compost faster.
Handa lies three miles (4.8km) off Sutherland's coast and is about 763 acres (309 hectares) in size.
The Scottish Wildlife Trust (SWT), which helps to manage the island, had the toilet constructed in 2012.
Its foundations are 2m (7ft) deep to stop it from blowing into the Atlantic.
Highland Council and the Scottish government contributed towards the cost.
SWT's reserves manager visited the operators of another remote composting toilet, at Stoer Head Lighthouse on mainland Sutherland, to get advice on improving the operation of Handa's facilities.
The trust said the island's loo had been "tweaked" and was now composting better.
Figures released this week by SWT show that 7,145 people visited Handa during its tourist season, which runs from April to September.
The number of visits came close to the island's record visiting figures of 7,324 set 12 years ago.
Handa is popular with wildlife enthusiasts.
The isle's thousands of seabirds include puffins and razorbills.
Great skua are another popular species with ornithologists who flock to the island, but the large birds are known to divebomb people and attack other seabirds.
A public toilet that cost £50,000 to build on a remote tiny island has been "tweaked" so it can better handle usage by thousands of tourists.