(Moved to laptop to prevent further lost posts!)
Some airlines such as Emirates and Etihad offer a "free" insurance which covers all the requirements of the COE and sandbox. But their cover for close contacts or asymptomatic infection is very limited. From memory its something like 100USD per day, whereas Bangkok-Phuket hospital charge 500 per USD day.
I saw one poster that failed his test on arrival and then paid 5600B for an Ambulance (in full hazmat) to take him to hospital for a second test. After failing that second test he was committed to Bangkok-Phuket hospital for 14 days at a cost of 271,000B. As he was using a french insurance provider he will need to pay frst and then try to claim later