Similar to last year looks like they have cheap one-day lift passes on certain dates. You have to select the 'Lift Passes' tab on the shopping box, choose month, then the pass and date on the next screen.
Good deal if you can go on those dates in July and August - that's peak season and usually costs way more. Last year I noticed they started increasing prices so I assume similar to airline pricing where it goes up depending on quantity or date.
I'd be hesitant about buying a ticket for June but their page on coronavirus says you get a full refund if they can't open. https://www.mtbuller.com.au/Winter/resort-info/about-mt-bull…
I used to work up there and the staff accom was so dank and cold that colds and flu's spread like wildfire. Not sure I would want to work there on a COVID year even if we get the official all clear.