Singalila National Park is protected forest land that requires you to have a permit before entering the forests. The forest entry fees cost INR 100 for Indian travelers and INR 200 for foreigners. There is also an additional cost of INR 400 for video cameras.
Most of the Sandakphu trekking package cost includes forest entry fees and permit charges, but do check the inclusions section of the trip you’re booking thoroughly to see whether it is included or not.