Transforming the hills behind Cringila into a major mountain biking playground will cost Wollongong City Council more than $5 million.
The new cost - which is five times that flagged in the first report on the plan - has been revealed in council papers to be debated next week.
Councillors are expected to vote to adopt the plan, which received widespread community support during its public exhibition period.
The council unveiled the draft master plan for the Cringila Hills precinct - an almost 40-hectare areas located off Jarvie Road between Cringila and Berkeley - in November, proposing to build an 11.8km network of mountain biking trails, a skill park and pump track.
The scenic but underused site will become a tourist and recreational attraction, which will also have walking trails, picnic areas and a new children's playground.
In that document, consultants Dirt Action said it would cost about $1 million to build the trails in three stages.
But now, the council says the first stage of the bike park facilities will be at least $1.5 million, while relocating and upgrading the children's playground will cost $540,000.
These works will be funded under council's 2020 budget.
The second stage, which includes construction of an asphalt pump track and a second stage of walking trails will cost $920,000, while amenity upgrades, park furniture and vegetation management will cost a further $1.2 million.
Finally, a third stage including car park construction, footpaths and public art will cost another $1.13 million, taking the total cost to about $5.3 million.
Only the first stage has been given a funding timeline.
During public exhibition, council officers spoke to hundreds of residents - including school children - about the bike park plans.
They said kids were particularly excited about the chance for adventure and nature play, and suggested the council include bubblers, free Wi-Fi, phone charging stations, shade (including planting of trees) and food and drink options at the park.
Overall, the council said there "was strong support for the master plan with people commenting that it provides for diverse recreational and social opportunities".
"Those who were not in support of the plan were concerned about the environmental impacts of mountain biking facilities, the mountain biking facility not catering to more experienced riders, contamination of the site and personal safety and access issues for surrounding residents," the staff report says.
At the request of the community, the council will include an amenities building for baseball facilities at Cringila in the master plan.