This is the USA eBay site, with US dollars. Close the US eBay site and
open the Australian eBay site. Look at your listings there, you'll find
the money is listed in AUS dollars.
Yes, it's a SCAM. If the vehicle is listed on some other website, not
eBay, but the seller tells you the purchase will be through eBay ---
It's a LIE and the seller is SCAMMING you and your aunt. Never pay for a
boat (or any other vehicle) with Gift ...