I can answer. That's fine.
Maybe you want direct figures, but essentially, retrofitting is always more expensive than starting out by being inclusive and accessible right from the get-go, so that's an example of how it might be expensive now to make schools inclusive and accessible. Here I'm talking about physical changes—so you have, maybe, ramps or larger, accessible toilets or classrooms that are light and airy, all of the things that make a school much more accessible to all children with different types of disabilities—but that obviously costs money. It's cheaper to do it right at the beginning if you're building a new school, making it inclusive and accessible to start with, than to do it later on. That saves money.
Also, if you think about the added cost to the wider society, the cost of not educating and of exclusion—and there are reports on this that we can share—is actually more than the cost of inclusion, because by excluding children you're obviously impacting society. Maybe their parents aren't able to work, so they, themselves, won't be able to grow up to have a decent job and gain income later on in life. That has a knock-on impact on the economy, for them and also for their wider family.
We should also think about the wider costs—less about the economic costs and more about the wider costs. Not having an inclusive society in general has an important cost for society. If the society is basically closed, inward-looking and not inclusive, that's not the society we should be advocating for, so I think it's also outside of the economic question.
There are studies that look at the actual rates of improvement for economic costs and for the GDP of a country by educating all children and not leaving out a section of children because it's not accessible.