I've been thinking of addressing such a technological problem myself. I was thinking of creating a basic list of technological advances, and people could simply branch out with their imagination.
If it was scientific, it might be free, but take a long time. (Such as Pasteurization) Some projects would obviously need a large funding, such as nuclear weapon/power development, mass production (As in, turning the nation's industry in this direction), or medicine. (Like Immunization Developments)
If it was an invention, it would depend upon the type. Electricity might be discovered accidentally, but using it as power throughout the nation would require investment. Cars may be invented for free, but making factories for them and producing them for the military will take resources.
If it was a military advance, this would most likely take investment. Armored Cars would require car development, and will require investment. Some weaponry may be inventions or discoveries, like bronze weaponry, but arming a nation with such items will require time and resources.
Example of system: (Bolded are general categories, italics are player decided advances)
Weapons > Guns > Pistol (Accidentally Discovered, Requires Investment to Arm) > Rifle (Investment) > Machine Guns (Investment)
Public Services > Public Health > Sewer System (Investment)
Industry/Infrastructure > Transportation > Dirt Roads (Discovery, Investment for Implementation) > Carts (Discovery) > Chariots (Investment for Military Use)
Only problem with such a system is the mind-boggling amount of advances, unless there is a vast generalization of said advances. But it allows for nations to customize in certain areas, and also allow them to pay more realistic costs than arbitrary 175 IC for Nuclear Weapons.
