I want to thank Melanie Breden and Doug Glancy for their suggestions regarding
the Like operator. After much research I finally stumbled upon what to do. The
solution is in inserting the ! character right after the opening bracket. The !
character immediately to the right of the opening bracket acts like a NOT
operator. Thus,

Sub MyTextBox_AfterUpdate
If MyTextBox.Text Like "*[!0-9$,.+-*/^()]*"
MsgBox "Sorry, you have entered and illegal character."
End If
End Sub

This will accept entries like $12,345.67 or
$52.27*(1.03)^2.5 and will reject entries containing an alphabetic characters
or extraneous symbols such as @ # { } [ ] \ ~ ` | \ <

Once again, thanks all.

-- Dennis Eisen.