I need to follow my own advice that I have been repeating to others. I need to focus on those things that are within my capacity to control and to let go of those things that I cannot. If xW wants to continue this war of bribing my S's and I find I cannot fiscally counter her, then I have to accept that that is just part of the terrain I am dealing with. I will simply do the best with what I've got. If that should prove to be insufficient to keep my kids from being swayed by materialism, then what can I say except that I did my best.
However, this is easier said than done, of course.