If you’re not picky Coles has own brand (Coles Ultra) tablets at a unit cost of .15 or the 1kg powder version is .39 per 100g.

Aldi theoretically has a few options for Logix brand in stock (.37/100g, .14, .25) but you’d probably have to try and check the stock for your store or give them a ring. They don’t always have everything. Plus the website really isn’t as good as 15 years ago when you could make a shopping list.