private void dgv_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
{
    dgv.EditingControl.KeyPress -= new KeyPressEventHandler(EditingControl_KeyPress);
    dgv.EditingControl.KeyPress += new KeyPressEventHandler(EditingControl_KeyPress);
}

private void EditingControl_KeyPress(object sender, KeyPressEventArgs e)
{
    if (dgv.Columns[dgv.CurrentCell.ColumnIndex].Name == "Summa")
    {
        if (e.KeyChar == ' ' && !dgv.IsCurrentCellDirty)
        {
            dgv.CancelEdit();
            dgv.EndEdit();
            dgv.CurrentRow.Cells["Ready"].Value = true; // дополнительное действие
            e.Handled = true;
        }
    }
}