All on 4 is very expensive. The price is set for all countries so you basically pay the same no matter where you go.
The next best option is a full denture that clips onto 2 pins that are screwed into your gum.
Top is about $8000 in Australia and same for bottom.
The main part of the cost is the 2 titanium pins which are expensive.
But it allows you to take the denture in or out at will.
And i have heard that this system has no fixed price so can be quite affordable in Thailand.
Just make sure you get a very professional dentist who checks your gums to make sure the pins will be firm and secure and that everything is a perfect comfortable fit .