You can buy these boots
on ebay for around $50 or so, but try this first. I watched numerous videos on repairing plastic
parts with baking soda and superglue for a strong bond. Google it, there are so many to watch. They use thin fiberglass mesh or screen to span the gap and ensure a permanent fix. I think cut up pantyhose would work well too. The best technique I saw was to reglue the piece together, then sprinkle baking soda, then apply thin superglue (you could overlay this area with your mesh right on top of the baking soda for simplicity). It will not break there again. The baking soda works as a catalyst, causing the superglue to immediately take on it's plastic form, pretty cool to see the transformation. Practice on some broken plastic you have laying around (make sure the plastic has been wiped down thoroughly with alcohol/mineral spirts, etc, whatever will evaporate and not leave a residue); once you're good at it, move on to the important repairs. I'm going to try this on my broken boot, I got a replacement, so I can mess around with the old
part (once i get around to making the swap, of course; I'm cleaning out my garage which my wife has packed with all kinds of stuff, just thrown on top for a decade, so it will be a while, I fear. The HORRORS!). But I will post my results, as you should do if you try this. You've got nothing to lose since the
part is already broken.