I think there could be confusion with fresh verses processed.
For fresh products (meats, fruits and vegetables), most of that sold in Australia is Australian as it can’t be imported due to biosecurity concerns. Australia is also exports a significant amount of our primary products as it can compete within the world market. Australia is know internationally as a quality, cost effective producer, and in some cases, foreign consumers will pay a premium for Australian products (milk power, avocados and cereals are examples).
Manufactured food products are very different as their treatment through processing has made them suitable to import (biosecurity risk removed or diminished). Such products can be imported and may have different quality to the manufactured Australian product.
The import of processed foods have been occurred more in the last 20 years, and some of that is to compete with low cost base retailers which have products which are dominated by imports (either imported as is, or imported ingredients mixed and packaged in Australia).
There are also some products which Australia does not produce or produce in commercial quantities, and have historically been imported (coconut products is a good example). These there are limited or no Australian substitutes.
The removal of tariffs about 40-50 years and more recently adoption of free trade agreements allowed Australia to compete in the international marketplace unimpeded and fairly. Fairly being that it was trying to compete with subsidised local produce or tariff added to Australian produce to make them noncompetitive.
Something all economics agree (yes, it is surprising as usually if there are two economists in a room, you will get two different views) on is that free trade (without tariffs or subsidies) has help the Australian economy enormously in the past 40-50 years (along with other things like floating the dollar etc).
The US has imposed tariffs on selected imported goods and are finding out that these tariffs hurt local industry and consumers as they ultimately pay more and local costs go up.
While tariffs and subsidies (which in effect nominating a minimum milk price is) is not good for the economy, consumers or our farmers in the long run.
As outlined above, what is needed is a free market not manipulated by any one group (government, processors, retailer, consumer etc). Such will ensure that all farmers receive on average, a good price for produce. Yes, there will be times where there is a abundance of the same product on the market which pushes down prices to possibly less than the cost of production, but this are not a norm and the taxation system allows farmers to spread thair income from good years to bad in such circumstances to maximise their average incomes.