Cheapest mode s with squiter transponder?

[nblight]

Building a new experimental homebuilt in aus which wont be finished for a couple of years but looking at the required transponders and it has to be equipped with a mode s with squiter (adsb out) transponder under the new rules, these all seem very expensive at the moment eg. $2500+ what is the cheapest solution to this as this piece of kit will be the most expensive thing going in the plane?

Thanks
Nick

 

[user 4289]

 

[BBerson]

 

[TFF]