To reduce the number of charges per transaction, see if your seller will send by Royal Mail or another carrier. If you can avoid purchasing items that are sent via the GSP (Global Shipping Program), then there's no separate postage/shipping charge charged separately.
The GST (10% tax) is unavoidable, however, if you're buying on eBay from an international seller. You may find the items for which you're looking from UK sellers (own website, or with a shop at which you can contact them by phone or email) who have a lower annual turnover of sales to Australian customers than the $75,000 threshold at which GST must be collected - or, if you can't avoid that, you may still be able to buy from UK sellers who will process the transaction in one lot.
There are other selling platforms on which sellers may sell, but you'll have to see whether the seller is considered the supplier for the purposes of the GST, or whether the platform itself is considered the supplier for the purposes of the GST. If the former, the seller collects the GST and forwards it to the ATO (and does all the paperwork); if the latter, it's the platform who collects it, etc., and in that case the GST component may well be charged separately for ease of processing.
