After splitting my inazone in scotland last year I fixed it with a small blowtorch (ie the type used for caramelising sugar) and a traffic cone.
Many people will say "cut some plastic off the back of the cockpit rim to make sure it's the same type / grade of plastic" but I found a traffic cone works fine.

It'll never be as strong as it was before, but it's watertight. I wouldn't take it on a difficult river (ie with rocks) in case of a collision - but it's fine in the surf etc.  I suppose that last comment depends on where the crack is, and how good your plastic-welding skills are!