Danh, it's all depends what shipping company you would use. If that's standard post then it's just 10% GST. If that's DHL/UPS/etc then they might take some small percentage for brokerage.
Have a think about splitting into two packages - scope and accessories. In this case you pay more for shipping but you can get below $1000 and therefore avoid GST etc. which at the end could be cheaper.
Also have a look at Astro-Tech AT60ED which is similar to WO ZS61:
https://www.astronomics.com/astro-te...d-doublet.html