If you want a cheap flight from Brisbane to Singapore, you've got zero airlines to choose from.
Singapore Changi International Airport is just one of the airports in Singapore. If you're not set on a specific airport, try changing your search from Singapore Changi International Airport to Singapore to see a broader range of flights – they might be cheaper.
You can expect accommodation prices to be higher at this time of year too. Last-minute deals do crop up, but it's best to book everything in advance to avoid disappointment.