This is cost the city spends on maintaining the land being sold (both trail, native, and grass) and the estimated tax revenue the property the sold property will generate.
The annual cost savings will be $13,895 and the tax revenue generated will be $3,965. The means selling the property will cost the city $17,860 per year. If you turned that into a fee it would be $0.32/per or $3.84/per year. If you turned that into a property tax increase it would mean an increase of $3.65 per year for a $600,000 home.