Doubtful you can get an exact number, but I believe Disney is using 3rd party CDNs, and those deals would have very high costs worldwide. Then you would have all the money they would be investing to produce original content. I would think those would be the 2 biggest costs for Disney+. Then there would be some other costs for things like the front end for the website/apps, and development charges (maybe hosted on something like AWS or Azure), but those costs would be tiny compared to the charge for the CDN and creating content.
I read some articles early on that Disney may build their own CDN eventually, and if they really are doing that, it would be an enormous investment on top of the costs of how Disney+ is running now.