$( "#amount" ).val( $( "#slider-range-max" ).slider( "value" ) );
и после $( "#amount2" ).val( $( "#slider-range-max2" ).slider( "value" ) );
добавить var result = $( "#slider-range-max" ).slider( "value" ) * $( "#slider-range-max2" ).slider( "value" );
$( "#how-much" ).html(result);