Thailand has over $30 billion in foreign exchange reserves. Someone who I cannot mention is allegedly worth over $30 million.
Meanwhile, the Astra Zeneca vaccine costs about £4 per dose (180 baht). So to buy 2 doses for everyone in Thailand would cost about £560 million. The government can afford that.
[The UK government figure includes buying about 5 doses per person and other investment in vaccine development capability. Probably a lot of waste, as is the norm with public spending from any party.]