I went through the same purchase decision recently and scoured the world for the best pricing - like you decided on Bilstein B6 (Eibach springs on the car already) following a chat with Volker from Alfisti.net who drives a GTV with B6's and has a Koni equipped colleague to compare it to.
I ended up paying 198 Euro for the rears + 45 shipping and 390 Euro for the fronts + 65 shipping, both from Squadra Sportiva in Germany (Alfisti.net). All up about AUD $1,100
I did find one very helpful supplier in the UK with the cheapest B6 front struts (AUD $541 for the pair) but shipping from the "old country" always seems to be so much more than shipping from Europe (i.e. quoted AUD $250 for shipping the fronts only).
Remember to keep an eye on the $1,000 customs limit - advice direct from Aussie customs was that the shipping is included in the calculation although if it is close they may let it through (i.e. if you are lucky.....). I split the deliveries by a couple of weeks - and added in a strut bar for some engine compartment "bling")