I looked into getting Flipper Fidelity Subs as they offered a better (although small) discount for multiple units.

Keep the total under $1000 to avoid the 10% tax. In saying that you want everyone to be in the same state and be willing to pick up as the shipping from you to them will negate any saving made by buying in bulk.

I may put a call out soon for a buy in Melbourne.

^This.

It basically works out to no discount on multiple kits from Pinball Pro due to (the seller's words), "the size and weight of each kit".

1 kit is 8lbs weight at $69 (the max rate) shipping and each kit ships in a separate box.

So you aren't really saving anything with a group buy from PP.