Its quite easy but time consuming.

Put the control what you want in the footer of your gridview.
Now bind the data of your gridview from the database.
you might be taking that data in a datatable or dataset right?
So now make one datarow. add the colums to that datarow which you are fetching from database.
fill that column values with your control values. Add those column values to row.
and bind the datagrid again with this new values.