That certainly would be an option. As far as I'm aware, it's only the facelift Altise and Sportivo that has a head unit that is not USB/iPod compatible, with the exception of the Grande that has the Satnav unit and cannot have iPod/USB connectivity. All other grades (except for the Grande) have the unit that is iPod compatible (unit shown in attached image).
The price of this unit as an accessory for the Altise/Sportivo would probably be around the $1000 mark I would imagine (haven't enquired about it myself). So if that were the case, a customer would be offered the iPod interface for $400-500 or the different head unit for double that. For some people, they see the $400 option as the cheapest but don't quite realise it may not be the most cost efficient. But also as well, this is mainly when ordering your car. If that were the case and they wanted the accessory unit on the Altise or Sportivo, they would then lose their steering wheel bluetooth controls as part of the package. This will then incur more costs if they want then, so then it starts getting to the point where the iPod interface looks like a better option.
Either way though, as an aftermarket upgrade, both will do the job, but it comes down to what they want to spend.
And Matt, as for your original question, an FM transmitter would do the trick but it probably wouldn't really be wise. Firstly the quality is not all the greatest (depending on how good your ears are) and secondly, you can't control the iPod through the head unit as you can with the interface kit.
thanks daryl,
will pass this on to my customer without the last bit though and give them one of our fm trans for a decent price.