The answer will always be, "more expensive than they are now". It's not like there will ever be a point at which more money, if available, could not in any way be used for some kind of drug research that might be useful. It's like saying "how much money do you need in order to keep from ever dying?" There will always be health problems, and there will always be some at least semi-plausible way in which we could spend…
The hypothetical situation you're describing has no connection to the reality of how drug research money gets allocated. We're not even ready to talk about how: - drug companies spend more money on marketing drugs than researching them - drug companies waste much of their research on copycat drugs rather than new treatments - IP law needlessly denies millions access to existing treatments by artificially inflating pr…
Innovations in pharmaceuticals is often incremental, not huge leaps forward. You have 4 different cancer drugs, each one adds 6 months of life for each launch and you end up with 2 extra years of life.
As well, copycats are needed, because not every drug reacts the same in everyone. If you need to lower your cholesterol, you have dozens of different statins to choose from. Some you won't be able to tolerate, others you can. Options are good, not bad.