I'm sure that for any given drug you'll see a pattern of later research costing more, but as a field, unless we happen to get lucky early on with figuring out the basic science (which we clearly didn't with neurodegeneration), we'll need years (or decades to centuries - emperor of all maladies is an excellent read into the amount of work and time it took to understand cancer to the level we do now) to understand what to spend money on drugs on, and we'll have to pay for all the dead ends there too.