I flight centre cheaper than Internet booking via American Websites?

[PLANT]

Hi there,

I booked an internal flights on Virgin America, Frontier, Westjet and all paid in US via Australian 28 degree card(it did the conversion).

So AA and UA you have to use the Australian website to book and pay?
On conversion via the website to AU they are charging so far $4-8+ conversion fee it seems?

If I paid via Flight centre using an XS card would I avoid this markup?

 

[PLANT]

Rang very helpful but not cheaper!