Why is the Dollar Amount different?

The dollar amount on your invoice will show AUD (Australian Dollars).  You have not been overcharged.   If you bought in US Dollars then the invoice will show AUD.  The price is exactly the same as shown when you were shown on the product and checkout page
Our site is hosted by Shopify and because of our location it's fixed to account in one currency which for us has to be "AUD" / Aussie Dollars.
That's why the invoice shows the dollar amount in AUD.
We are based near Brisbane, Australia. We have the kit in stock and can ready to ship asap. The quickest method is Fedex Express shipping, which takes 2 to 4 business Days.
The website is set to automatically show the product prices in your local currency depending on your location.  So if you are in the USA it would automatically show the prices for you in "USD", US Dollars.
The payment is processed in your selected local currency, so when you checkout you are charged the same US dollar amount that you were shown at the time of purchase. 
The only difference is just that the invoice sent shows the equivalent in "AUD",  Unfortunately it's something that is fixed by shopify who host our site and we can't change it.  I think if you paid with paypal it will also show the AUD amount.
If you take another look at the product page, at the top of the page there is a flag.  There you can change it manually and it will change the prices to show whatever currency you want.
If you please check your card statement you will see we did not overcharge you or change the price but no worries if you want to cancel the order, please let me know.