I've never calculated shipping on parts value, always based on "what would you pay for shipping if you ordered outside of the group buy". Skandix shipping is flat-rate (except for "XL" items, which are excluded from the group-buy anyway), so everyone who participates pays an equal share of the total shipping.
i.e. everyone pays: (individual shipping cost) / (the sum of individual shipping costs) * (group buy shipping cost)
Hopefully that explanation satisfies everyone. If not, all I can really add that as it stands currently, this is what you can expect:
Shipping (group buy): €28Shipping (no group buy): €140Group-buy saves you: €112 (~$175)
Some people in the group buy spend a bit more for domestic parcel forwarding from Sydney, but even then you're still going to come out miles ahead.