I went through your mod's files to add a few things that affect dev cost in my modpack and found that you didn't add a few things from the vanilla - Renassaince and Innovativeness, so I added them. Feel free to add them in the next update, I don't mind or care.

link to the changes https://github.com/dnarik/Rebalanced-Automatic-Development-dnarik/blob/master/Changes%20I%20made

Also I've seen another similar discussion of this mod, "I made a small number of changes", and I suggest maybe implementing local_development_cost in some way, maybe not directly 1-to-1 but, for example, if local_development_cost is +50%, make it +20%, +75% becomes +33%, +100% becomes +42% and so on, or maybe some other kind of curve. There is lots of balancing that can be done with this mod, and it is, understanably, hard to do. If you would like me to, I can share my results for that, if I decide to do some testing for my own modpack anyway