If you want a cheap flight from Hanoi to Singapore, you've got zero airlines to choose from.
You can use the filters on your search to see more flights and find cheaper rates – Singapore has more than one airport. So if you don't need to fly into Singapore Changi International Airport, it's worth checking your other options.
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.