There are multiple options for big zoom bridge cameras from Canon, Panasonic and Nikon as well as Sony.
The pack leader is the Nikon P1000, with a 125x zoom. several others offer 65x.
They all use a small 1/2.3" sensor, so they need plenty of light and good stabilization to give good images.
Here in the US, the Sony is available for about $350 US, about a third the price of the P1000. The earlier P900 with 83x zoom is priced around $525.
Issues to consider are the quality of the stabilization and of the viewfinder and LCD screen, plus the speed of the zoom. It is frustrating to try to get a shot while the camera is gradually waking and getting ready.
Note there are other cameras with bigger 1" sensors such as the Sony RX10 IV, 'only' 25x zoom but a much more robust camera.
Arriving at a choice is a thicket which makes binocular selection seem a kindergarten play. Perhaps best to stay uninvolved and let your son decide for himself. Hopefully it is his money and his learning experience.