In Australia that's either an ultralight tanker, which would cost around $100k USD today but with far lower 550L capacity and a lower throughput pump than a heavy tanker, or it's a command vehicle, and its modern equivalent would cost about $60k USD but have no pump or water tank. The ultralight tankers are mostly used for getting to fires faster when they're small, dealing with inaccessible terrain, or just being an extra vehicle during blacking out etc.

The problem you're always going to run into is that your truck needs to haul around 10 tonnes of water and protect its crew. You can stick a pump on the back of a hardened ute, but then you need to leave and find water 20x more frequently plus your pump is a dinky little water pistol, or you can drive a commercial water tanker into a bushfire, but then your driver needs to be unusually brave and no longer have much to live for.

I accept that firefighters are getting ripped off, but it feels like maybe 5% to 20% of the cost could be reduced, and then you're still dealing with unaffordable equipment.