If you just change the head lights and bonnet the front bar will sit under the head lights and will not line up properly.
To make it fit and look decent you need:
Head lights, (Expect to pay from a wrecker if your lucky enough to find them $300-500)
Bonnet, ($200-300)
Front bar, ($250-600)
Reo ($200-300)
Wiring for fog lights (if you dont aleady have them on your S1)
Then on top of that you need to paint it all.
Polish the head lights and wack on some eye lid covers.. will prob cost you $80 all up.
Cheers
Johno