How do I Populate a Grid based on a select in a combo box in the first column of the grid

1. Is that when the initial list is loaded it is setting the initial value of the list/combo box value to the next item in the list but I would like all of the list/combo boxes to start with the same initial value unless it is an existing order so how do I make each list start at the same item (in this case blank).

2. Next when an item is selected how do I catch that value so I can populate the price cell. When I am using a fixed list I don't have any issues but when I try and use the combo box I can't figure out how to determine that only the combo has changed not any of the other fields.

Thanks in advance