How about: "money does not buy happiness, but it can mitigate a whole lot of the misery associated with lack of money".
For an analogy - it's no more fun swimming in a 500 foot deep lake, than a 50 foot deep lake, but a 3 foot deep lake with rocks and waves is painful and dangerous and no fun.
The baseline of money that eliminates misery ( == "buys happiness") is that which takes a person from "really poor" to "modestly middle class".
I like that example. I use a similar analogy to that frequently. If you are in a room with a ceiling that is even a few inches over your head you don't have to stoop at all. It doesn't necessarily benefit you if the ceiling is 3 inches over your head or 10 inches or 10 feet (with respect to walking that is - add some room for up and down etc.) On the other hand things become tremendously difficult if the ceiling is even an 1/8 of an inch lower than it needs to be. In that case you have to stoop and you can't walk normally.
For an analogy - it's no more fun swimming in a 500 foot deep lake, than a 50 foot deep lake, but a 3 foot deep lake with rocks and waves is painful and dangerous and no fun.
The baseline of money that eliminates misery ( == "buys happiness") is that which takes a person from "really poor" to "modestly middle class".