You should be able to list on US eBay by simply being logged into the site when you list - I'm not sure why it would default to an AU listing, so all I can suggest is perhaps ensuring you're logged out of the AU site in any other tabs, or maybe even try using a different browser for listing on the US site.

They do have lower insertion fees, but just keep in mind that FVF is also charged on postage, and there will be different policies your listings will be subject to.