updating Currency field in a table

Hi,
while populating the data on a form i am formatting the currency field with  "{0:c}".  if it is  4650 then it will display like  $4,650. because of the $ sign and comma, i couldn't able to update this field to the database. can you guys give me some advise.? Thanks for your help.  Here is my text box field i am displaying the currency field.

@Html.TextBoxFor(f => f.Invoice.GrossTotal, "{0:c}", new { @class = "input " })