Op- I haven't quite read all the thread, because quite frankly, some of it has been absolutely vile, but I hoped that this might help with what I feel may be the root of the issue:
I got minimal maintenance from xh, for a few years, then nothing at all, (particularly after I met DH). It enraged me, but not because some money would've helped- of course it would, but, y'know, I managed- but because it meant that he could do precisely what you are worried about. He bought ds1 every gadget under the sun- a mobile phone (when ds1 was 9!!), iPad, laptop, games machines, iPod. It upset me so much, that I could barely give ds1 what he needed, let alone all these expensive gifts.
But here's the thing- although ds1 loved his father (xh died, last year)- it wasn't the expensive presents he remembers best now. What he remembers- and remarks upon even now, at the age of 19, 15 years after my divorce- are the things we did together. What fun we had (even with little money). That I was there to help with homework/go on school trips/soothe him at night when he had bad dreams. And the present he remembers the most fondly is the (cheap) radio cassette player I gave him one Christmas.
I know how you feel. But you sound like a good, caring, loving person to me. Your children will grow up knowing the right things, and will recognise any expensive gifts from your xh for what they are.
I hope things go well for you.