If you are talking about the ceramic shaft that holds everything together being broken, I wouldnt bother. There is so much torque on them that they will probably break again at the weak point. Sometimes, if you can find the manufacturer, you can find replacement parts. I dont know if you could just buy the shaft of if you have to replace the whole impeller, but it's worth looking into. If you cant find parts, then I would go get another as soon as I could afford it.
Sorry to be a wet blanket here, but I've tried fixing broken shafts before. It isn't worth the trouble.
Why do I love fish? Because every time I stare into the little world I have created for them, every problem I have just floats away....