Buying weapons from your global security partners is part of a larger geopolitical picture/strategy. The cost is almost secondary. Look at who the US sells weapons to, what countries are banned by us weapons export ban laws. Look at who Russia sells weapons to. There is not a whole lot of overlap between the two countries.
Posting countries and dollar figures is part of the picture, but does not tell the whole story.
And when there is an overlap, people freak out. Just take Turkey as an example. They almost got kcked out of the F-35 program after buying Russion air defence systems. The US feared the Russians could learn too much about the F-35.
Posting countries and dollar figures is part of the picture, but does not tell the whole story.