Your calculation will depend on your particular values.
Example #1 Market value is equal to assessed vlaue (property has no cap)
Initial market value $200,000
Initial assessed value $200,000
Final assessed value -$170,000
Reduction achieved $30,000
Tax rate from previous year X 3%
Taxable savings $900
Contingency fee @ 35% $315
Example #2 market value exceeds the assessed value (property has a cap)
Inital Market $210,000
Intial assessed $200,000
Final assessed - $170,000
Reduction achieved $30,000, not $40,000
Tax rate from previous year X 3%
Taxable savings $900
Contingency fee @ 35% $315