Cheapest way is to splice another connector in to the D2B (fibre optic) loom as it seems to me that breakers charge a fortune for D2B cables. The voice module is the same across the S-type X-Type and XJ. As you say, dozens on ebay.
Denis (the jag den) on this forum will be able to sort you out the module cheaper than any of the commercial breakers and I can assist with the D2B cable, either as a spliced connector or replacement loom , if it will help.
Fitting is simple but you'd need a session on diagnostics unless the module you use exactly mirrors the kit in your car. Takes about 5 minutes.. If you were passing Wolverhampton / Penkridge way, Denis or I could do that for you.