Postage is indeed the killer for us Aussies, especially when items come from those businesses that are not VAT registered, and I assume Nick is not due to the UK small business VAT rules etc. So we don't save the VAT when we purchase from outside the EU like we would with a larger company, since that can help to offset the postal costs and make the final bill less shocking.
For those who don't know, postage these days for large items is charged volumetrically, WxHxD thru an algorithm, then compared to the actual weight and the larger cost applied. This is especially relevant for airmail where space is at a premium. The days of sending light-but-large fairings cheaply is gone sadly for us, but the postals arent now losing money on those items LOL Depends on how you look at it
Do bear in mind that for those not in a hurry, the UK still offers Surface mail, many dont (USPS comes to mind). It takes about 3months and for something like a used fuel tank should really be mandatory. Sometimes it can be quicker, but bank on 12weeks or so.
Buying in bulk is a good idea, especially if items can be packed cleverly to save room in the box, i.e. where 5 takes up only 10% more room than 1 item. Then the shared postage costs work well.
All this is just my 2c and offered for your understanding... IMHO, and having worked for postals worldwide, the pick of the bunch right now for those of us buying parts for our bikes... is.... {drumroll}... Germany. Yep, that's right, their postal system is distributed and as such they have not yet embraced the changes that the others have, and lets face it, being slower than USPS and RoyalMail is a worry if you're in the industry LOL. Buying from here means we get the local 20% tax off, then their post is cheap as chips. Right now you can have parts landed here for less than a German buys them in the same shop you ordered from if you search around. This will change, so make use of that knowledge while you can LOL