MOB, I hope this comment doesn't come across as harsh, as it's kindly meant, but part of your second post makes me think there may need to be some mental adjustment on both sides of this situation. I can clearly see the adjustment needed on your DD and SIL-to-be's side, especially as you are paying for the wedding and as others have comments on that, I won't, but I wanted to offer you another perspective.
I've never been a MOB, or even (for another few months!) a mother, but I have recently been a bride. One thing that gradually dawned on me, maybe too slowly, is that a wedding, for all it's a celebration, is also a landmark in a mother/daughter relationship, and not necessarily a wholly comfortable or happy one for the mother.
As children grow into adults, they increasingly develop and lead their own lives. The relationship with their parents evolves. As much as the mother/daughter relationship is never "replaced", when a woman marries, she is taking another person, her new husband, to be the most important/central "other" in her life. This process has almost certainly happened gradually over time, but the wedding, and the planning of it, can be quite a stark illustration to the parents of the couple of the extent to which their children now lead lives independent of them.
As much as we women dream and plan of all the wonderful things we hope the future holds for us and our families (and I'm already dreaming and hoping about the future life of the little girl I'm carrying 
), ultimately, it is their life to live as they choose and there comes a point where parents have to take a step back. You have long dreamed of helping your daughter plan her wedding, and it sounds as though she wants your involvement too, but is there a chance that in your excitement to be living part of your daughter's life that you have long dreamed about, you may not be giving quite enough recognition to the idea that it is their day (your daughter and future soon-in-law's) and not yours?
You comment that "I can see he's thinking he's doing the right thing by getting deeply involved in all the plans, but in fact, he's squeezing me out". My gut reaction reading that sentence was: "but he's entitled to be more involved in the plans than anyone else (except possibly the bride!), it's his wedding and anyone else is only entitled to be involved to the extent that he and his fiancée want them to be!". Your financial contribution to the day obviously alters this balance somewhat, but I imagine you gave your generous contribution in the hope they would have the wedding day that they would enjoy.
I think part of the difference in perspective between mothers and daughters in your situation may be a generational thing. I cottoned-on, rather late in hindsight, to the fact that my mother had had very little say in the organisation of her own wedding as at the time the bride's parents generally arranged (and paid for) everything; and against that backdrop, I think she had simply always assumed, with no domineering intent, she would have a significant deciding say in my wedding. Whereas, my DH and I were starting from a polar opposite perspective, of assuming that it was "our day": our preferences and opinions would be the deciding ones and others' involvement would be subsidiary to that (it is possibly relevant that we were also paying).
I'm not saying that either view is better, or preferable, and I think the egocentric approach of many modern couples (myself included) is certainly very open to criticism and doesn't always reflect well on us, but in my own wedding planning I came to realise that some of the difficulties my mother and I were having seemed to stem from the fact we were starting from totally different perspectives. Our expectations of the roles each of us would play simply didn't match-up.
I hope this may help you to understand where your daughter and son-in-law-to-be are coming from and maybe interpret their behaviour/reactions in a different light. Good luck. I hope you manage to get things sorted out and enjoy the planning, the wedding and all the lovely things that I'm sure the future holds for your newly-enlarged family.