£65 inc VAT I paid from the dealer, took a couple of hours to change.
Steps to change GT door handle, the 147 is pretty much the same.
1. Remove all screws on bottom edge including the one in the light
2. (Driver's side only) Remove screw in middle of door card below arm rest, this screw secures the electric window switch node.
3. Remove electric window switch node, this just prises out, disconnect plug(s) to node.
3. Undo allen bolt that is revealed by removing switch node.
4. Use a very small screwdriver or maybe a stanley blade, to lift up an edge of the blank in the interior door grab handle, once you have something to get a decent screwdriver behind prise out the blank. These are easy to mark as is the handle itself, some members order replacement blanks in advance and simply drill a hole in the existing blank and lever it out. The part numbers are RH #735351270 and LH #735351271 or #71775574 for the pair.
5. Undo allen head bolt revealed by removing the blank.
6. Pull off interior triangular trim that covers the mirror fixings.
7. I also removed the mirror, 3 x torx bolts but looking back I don't think this was necessary.
8. Remove popper from interior, top, rear edge of door. If you can get this off without breaking it, let us all know.
9. Use a small head screwdriver to prise the circular blank behind the interior handle that opens the door.
10. Remove screw revealed by removing the blank and remove the black plastic door handle surround.
11. The door card is now just held on by the poppers on the vertical edges, carefully prise the edges away from the door, these seemed to be much more forgiving, not one of them broke.
12. Disconnect door light connector.
13. Grab both edges of the card and rock it up and off the door.
14. Peel the rubber at the top rear edge of the door from around the 1 popper revealed by removing the card and the 3 poppers above the lock mechanism, I didn't try to prise the poppers out after breaking the one on the top. It's not possible to do the top one this way it has a much larger head.
15. Lift the rubber and exterior weather strip that runs the length of the exterior top of the door up and off.
16. Remove speaker(s)
17. If you hadn't already read in the forum, be amazed that your Bose system (if fitted) has no tweeter, but there is a coiled up connector for one.
18. Use a Stanley blade to cut the adhesive that holds the foam sheet in place, needs to be folded out of the way about halfway down the door. Use a blade to cut it neatly round the sockets for the door card poppers....these didn't look they were going to move.
19. Remove window. Sounds drastic but it's only 2 nuts and one bolt. You may need to reconnect the switch node and position the window so you can get at these through the holes, 1 x 10mm nut on the bottom front edge, 1 x 10mm bolt and 1 x 10mm nut directly above it on the bottom rear edge. Mark the position of the nuts/bolt with tippex or similar so that when you refit the window it goes back in the same place.
20. Lift out the window.
21. 10mm spanner in your piano tuner's hand to undo the nut behind the exterior door handle hinge.
22. Undo 1 x torx bolt adjacent to the 3 x poppers revealed by removing the rubber and weather strip.
23. If you're doing the driver's side (like me) there are 2 x rods connecting the door handle to the lock mechanism. If you peer down into the the door you can see the clips on the rods connecting them to the lock mechanism. Unless you have forearms like Popeye you can reach in and push the clips outwards to release the rods.
24. The door handle is now free to be removed, it first needs to slide toward the front of the car and then wriggle the handle out of the hole. If it's proving hard to get it moving insert the bolt from step #22 a couple of turns and tap it gently with a hammer.
25. Swap the lock barrel over. To do this you need to release the curved metal armature that is rocked when you pull the door handle. It has to be levered out of the black plastic cradle that passes from the outer to the inner of the handle. Undo the 3 x screws on the inside of the handle, finally there is a U shaped clip that needs to be prised out that releases the lock barrel from the holder.
26. In true Haynes style put it all back together in reverse order. It was proving difficult to get the handle back in the hole with both rods connected, I found it easier to remove the rod that operates with the key, insert the handle and then push the rod in using long-nose pliers from the the top. You'll need some sort of adhesive for the foam sheet, a hot glue gun is great for this.
The part number for the popper in the rubber on the rear, top edge of the door that broke is 14591987... 0.90p (ish).
Additional. Can't believe it's getting on for 4 years, time flies.
In that time a cheaper fix can be had providing only the front hinge has broken. If the door handle has come off in your hand you'll have to go through the above.
Fiat now provide a replacement hinge for the Fiat 500 door handle and is pretty much identical to the 147/GT hinge part No. #51939041 (same part number for both sides). I've read this replacement part is only good for the GT and the Facelift 147 as there's a difference in the in the way the hinge mounts to the handle. You can see in the image below the screw hole where it attaches to the handle is at an angle...
...whereas the pre FL 147 (and possibly very early GTs) has a hole at right-angles to the hinge.
As far as the steps above are concerned the door card still has to come off so as to undo the nut on the broken part of the hinge. It'll be tricky to remove and replace the hinge with the handle still on the car, you'll need an angled screwdriver or, if you have one of those screwdriver bit sets, use the appropriate bit and a ring spanner. For the time it saves and not running the risk of scratching the paintwork it's not much more bother to take the handle off.
Some have reported this replacement causes the hinge end of the handle to sit proud of the door by a couple of mm, others say it's a perfect fit. Maybe those reporting it sitting proud have fitted it to an pre FL 147 or early GT, despite all the threads on the subject it's not clear what the issue is.
All the best