The answer to this question depends on what is most important to you - price or speed. If speed is the most important requirement then choose express+tracking. If cost is more important then select economy. The economy option does not have tracking and is not available for orders over US$250.
Because of recent price rises by USPS, for most packages over 4 lbs (1.8 kg) it is normally cheaper to ship by express than economy shipping.
There is no sea mail to Australia from the USA, but for large orders sea freight is an option. It is not cheap than UPS for smaller items (less than 100 lbs), nor very fast (8 to 10 weeks). Please use my shipping cost calculator for the approximate cost of using sea freight.