Money spent on something that is extremely likely to keep its value, like the original of a widely-known and -loved artwork, isn’t “extra cash” in the same way that money spent on a thing whose value can be expected to dwindle (like, say, a car) is. Of course, you have to be on track to cover the monthly bills before you buy either; it is “extra” in that sense.
Not that you don’t know all this. Also, sweet Neal Adams piece.