The situation is grim for solo cruisers in Australia whose most affordable option is to share a cabin with a stranger. Only luxury lines and river cruise lines offer no single supplement deals. The problem is that most local ships are targeted at couples, families and groups, and cabins are priced accordingly. If you want a room to yourself, expect to pay around twice the published cruise fare to cover the cost of the "missing" second passenger. Cruise lines simply want to make sure they are making the same money for the cabin whether it is used by one or two passengers. However, there are some tricks of the trade.
Cruise lines will sometimes waive or reduce the single supplement to fill empty cabins, but this is almost always for overseas departures, and often on more expensive small ships or river cruises. From time to time, Australian cruise lines do release single fares that are cheaper than the standard twin fare. This is usually for "distressed inventory" -- cabins they are worried they can't sell -- 90 days before departure when final payments are due, and people tend to cancel. These deals may be 150 percent of the full cabin price instead of 200 percent and are rarely advertised. Basically, you have to be lucky to stumble upon them by continually searching websites for such pricing anomalies.
One way to find out about good deals without too much web-surfing, is to sign up for individual cruise lines' deals and special offers. Websites usually have a drop-down page that you fill in with your name and email address -- while you might get lucky and find a cheap gem hidden amid all the marketing material, the downside is you'll be bombarded with info.
Some sneaky people try another practice: the 'no show'. This is when you find a good twin-share fare, book yourself and a friend (who has no intention of coming), and then your friend doesn't show up on the day of boarding. So, you have still paid for two people, but you get the room to yourself. No, you certainly don't get a refund for the person who didn't turn up, but your discounted twin-share fare was cheaper than paying for the single fare (the full twin-share price).
If it all sounds like hard work, too dodgy or high-risk, generous people often share bargains they have found online. The El Cheapo Cruises Thread on Cruise Critic's Australia & NZ Cruisers board has been running since 2014 -- skip to the last page for the most recent posts. Cruise Critic also promotes solo specials on our Solo Basics article.