this is pretty much true - ours will break even-ish this year compared to what we'd pay buying the items from the local woolies - the win is the flavour. and the instant gratification i guess - tonight for instance, we were having fried rice and took peas and snow peas out of the garden and into the pan. no having to think it through at the shops or dash down there - it was a case of having it when we needed it. and having healthier snacks - i'd much prefer DD to have strawberries or snow peas fresh from the garden instead of yogurt or sultanas - but we still have those in the house as healthier alternatives to sweet biscuits and chips and stuff....
Flavour is well worth it along with the nutrient content, I just don't think "grow your own" should be pushed as a cost saving measure (have seen it in many articles, advice columns etc). Possibly long term, once the main set-up has happened, especially if you (generic you) seed save and have worked out what grows well for you, along with what you actually will eat, it would then save money.
Growing your own herbs is worth it though and a great place to start for many people.

I was shocked when saw on a Bunnings receipt that vegetable seedlings incur GST Logically if the output is GST free, then surely the plant would be as well.