I find the assumption that DB's cost less to educate strange:Of note, most modern first world people don't have as many children as they want.
Australians want more children than they have, so are we in the midst of a demographic crisis?
I think Dragon-Blooded education is really going to be cheaper per-capita than real world high class education. Dragon-Bloods learn at Exalted speeds post-Exaltation and pre-Exaltation can be taught by mortals just fine. With DB Charms an average Dragon-Blood is going to have a lot more wealth than an equivalent mortal noble would have. Pregnancy is inherently less debilitating and dangerous for Exalts than for mortals. Most of the resource constraints that keep modern fertility so low are gone in the Realm. Most of the constraints that kept historical growth rates down are also gone for DBs, as they have access to Medicine Charms and the ability to supply plenty of food through either their own abilities or the time honored practice of making mortals do it.
Certainly I would not expect factory farming of DB babies or any such shit, but I'd expect the population growth to be fairly high and steady for any group with the traits possessed by Dragon-Bloods.
1. Dragon-Blooded learn just as normal until Exaltation, I.E. until at least age 10, with most Exalting only in their teens. In other words, most of their most crucial and formative years are spent as mortals, and so they will learn like mortals until Exaltation, at the same cost.
2. After they Exalt, well, they're Exalted. You're not having them study the same material as mortal students, just faster. Even when a mortal and an Exalt go to the same course in the House of Bells, in the rare case that a mortal gets to go there, the mortal and the Exalt will have a different learning experience: the mortal will be training his mundane fighting skills and memorize conventional tactics, while the Exalt will be training in the use of combat and War Charms. Not merely developing those Charms, but also training in how to use them best. This is training that the DB will have to take, but the mortal does not, because it's not relevant for him to train in abilities he does not possess.
This is before going into things like accounting for Anima Flux, the legendary tempers of the Dragon-Blooded, or the fact that Exalts are more likely to train abilities to 4 and 5, which requires quite a bit more than simply learning the same material as a mortal, but faster, as you're looking at better teachers, access to more advanced study materials, and potentially time to train and advance personal enlightment for optimal use of Charms in the relevant field. You don't train to 4 or 5 by learning the same material and from the same teachers as everyone else who got a 2 or 3, otherwise the school would be pumping people with abilities at 4 or 5.
If you are sending an Exalt and a mortal to the same training, then you'll get a mortal and an Exalt trained to mortal levels. Yes, the Exalt will finish his training earlier and at probably reduced effort, thus less cost. This does not mean that you have a well-trained Exalt, it means you have two well-trained mortal-level professionals, one of whom happens to be an Exalt.
To train an Exalt means to train an Exalt. The fact the Realm adds all the trappings of nobility to the matter only helps to increase the financial burden here.