Automatically sub-total a list and export to files

The file that I have attached has the run sheets of truck drivers, which company they are working for and how much money they are owed (the money they are owed is in the GST column).

What my company needs to do is to create a tracking sheet for each month for every company with a sub total of how much we owe them.

As an example, in the file I have provided, if you filter all the dates in between 1/9/07 and 1/10/07 (so all the dates for September) and then filter Company to 'Cole Moore & Sons'.

So what you see is all the jobs that Cole Moore & Sons has done for our company in September. What we want to do now is create a sub total at the end which calculates the GST column and then save it to a file, which we can then e-mail the company to say 'This is how much we owe you, is this correct'.

But since as you can imagine, filtering and adding the sub totals is a long process, is there a way to

1) Have a sub-total show up automatically when you filter by company

and

2) Have some kind of formula or code which would filter every company within a certain date range adding the sub total and save it to a folder named 'Sep' for example. This would be the killer if it can be done.

The reason being is because the real file is much larger than i could fit here, and it would be a long process to do this manually, that is filter the company, type in the sub total, and save it to a file, as this is done every month.

Any help would be appreciated.

Thanks
Kosta