Hi, I've just sent a parcel to Oz using Royal Mail. It weighed under 1kg and cost £23. The Royal Mail website seems to indicate that a 2kg parcel insured up to £250 would be about £25. I think the key is to keep it in the "small parcel" size. I managed to fit close to 100 28mm figures into a "small parcel".
Good luck. I've had exactly this same problem when an Aussie bought a massive ( and heavy) 15mm FoW army off me on E-Bay, and didn't realise the quoted £15 P&P was only for UK. I think it cost him nearly £70!