If it is light and inexpensive, I wouldn't bother with the custom form.

If the chips are light and strong, I'd wrap them in paper and paste them inside a regular envelope, and if the parcel is no more than 1/4" thick, it would cost [first class letter rates] (including the 20-cent surcharge): 1 ounce $1.18, 2 ounce $2.02, 3 ounce $2.86, 3.5 ounce $3.70.

For other first class rates:
http://www.usps.com/prices/first-class-mail-international-prices.htm

(Australia is in price group 3-5.)

When I said "If the chips are light and strong .. ...". I meant to say, of course, "If the chips are inexpensive/common and strong... ... .. " I've sent many modern, strong chips that are worth under $10.00 that way, and never had a problem -- nice inexpensive way to send them. Of course, if the chips are frail and/or valuable, I sandwich them between stiff, strong cardboard and send them first class PARCEL rates, or package rates.

Robert