Annual cost calculation based on date

HI All,

Need help to get the formula for calculating cost based on working days in a month (networkdays) based on date we are giving in DOJ column(C)

in attached sheet, given 5/15/2013 in colum C , so before given date & Months value should be "0" and need "May" month remining working days and next months cost .

i used below formula but not working

IF(IF(TEXT($C6,"mmm")=TEXT(F$4,"mmm"),160/30*NETWORKDAYS($C6,F2),0),IF(TEXT($C6,"MMM")<TEXT(F$4,"MMM"),160/30*NETWORKDAYS(F1,F2),0),0)

Thanks,
Sekhar