It's hard to do in Word. Here's a macro that will format numbers in a table. Perhaps you can tweak it:
Sub ApplyNumberFormatToTableCol()
Dim tbl As Word.Table
Dim cel As Word.Cell
Dim NrRows As Long
Dim colCurCol As Long
Dim counter As Long
Dim sInput As String
Set tbl = Selection.Tables(1)
' The following is on one line
colCurCol = Selection.Information(wdEndOfRangeColumnNumber)
'This is one line also
NrRows = tbl.Range.Information(wdEndOfRangeRowNumber)
For counter = 1 To NrRows
Set cel = tbl.Cell(counter, colCurCol)
sInput = cel.Range.Text
sInput = Left(sInput, Len(sInput) - 2)
If IsNumeric(sInput) Then
sInput = Format(sInput, "$ 0.00") cel.Range.Text = sInput
End If
Next
End Sub