Flooded deep cycle batteries are somewhere between 7000 and 9000 THB if I remember. It also depends on how many Amperehours they have. AGM and Gel batteries more expensive. Our system is 400/230V.
Generator, as I said, is for backup and will not run much if everything works as it is supposed to. It is expensive, like you say, and it is a security and peace of mind that I like. You can, of course, decide you can do without that and save the money. But I know, with our first system, how it feels when the system goes down and you do not what happened. Following Murphys law this usually happens a rainy, dark night.
Implementation into the system of the genny is fairly straight forward. Power lines go to the ATS (Automatic Transfer Switch) box and then to the inverter. If the power goes down, f.e. if the batteries go below 10.7V, the ATS will tell the genny to start. And when the batteries are recharged, the ATS will restart the inverter and shut down the genny. So I do not have to do anything manually.
At least that is how it should work. But now our genny is too small and cannot charge the batteries. It will start from the ATS to feed the house so we will have power until the sun has recharged the batteries. Then the genny will shut down.
Hope I made myself clear. :-)