The good news is that it is possible to resolve the issue.
The bad news is that it will take a lot of time and effort.
How much the unit cost, and how much time you're prepared to spend on it will be for you to decide.
You will need a reasonable test meter, and know how to calculate current in a resistor, given the voltage.
In the first place you need to be able to generate known AC currents, and the easiest way to do this is with a low voltage transformer and some chunky resistors.
Start with, say, 1amp, and put something like 1kohm across the sensor's terminals. Close the core on the current carrying wire and see what you get. You want to end up with about 10V at the maximum current you expect to measure.
This was the easy bit.
The hard part is converting that AC voltage to a DC signal in the range 0-5V. A conventional bridge rectifier is of limited use as it will lose 1.2V straight away and give you all sorts of linearity issues. It is possible to make zero offset rectifiers with Op-Amps, but the easiest method is to use dedicated RMS-DC chips which aren't too expensive. They are also very accurate.