Setting a GridView column to read-only is not possible via the Form designer or using action parameter, but you can do this using code.
This sample code (in the form designers ASP.NET editor) will sets the TextBox of the second column (Quantity => Index 1) to read-only using the HTML readonly attribute.
protected void Page_PreRenderComplete(object sender, EventArgs e)
{
base.Page_PreRenderComplete(sender, e);
((TextBox)this.EXPENSES_GRIDVIEW.Rows[this.EXPENSES_GRIDVIEW.EditIndex]
.Cells[1].Controls[0]).Attributes["readonly"] = "readonly";
}