dataGridView custom sorting

Question

I have a column which can take values like these:

152,678
22,001
3,571
78,055

Now thats how it would be sorted right now, seen as strings
But I want to sort them as Integers.
(The value "N/A" can also be present, i want that to count as zero.)

Right now the column is Sortable: Automatic

I've read the CustomSorting article at MSDN, but I dont really get it fully.
How should I do this?