I noticed that you have submitted the same query in a ticket, as I have already answered in the ticket, I will post the reply here as well in case someone else has the same question.
The default editor of the grid is a plain input element. Thus, formatting is not supported with it. If you need to format the value in edit mode, you will have to create a custom editor template which contains a NumericTextBox with a specified format setting.
In other words, in the ~/Views/Shared/EditorTemplates folder, add a view with a name "Number.cshtml" and within that view create a NumericTextBox as follows:
Please note that you will also have to decorate the field of the model with the UIHint attribute to specify that this view is its editor.