Israel is a US client state. Like Saudi Arabia. Obviously useful if you want control over the world's energy markets, a basis of all economies. (There's some other reasons too; like the US linked it into its high-tech industry.)

Regarding billions though, the US has all the wealth it could ever want. It simply wastes most of it. Everyone could easily have a 15 hour workweek or whatever. The phenomenon of unemployment could be considered a decadent joke (where idle hands can't find work though they're looking for it, and there's much to do).