If I fell back on the medicare formula at a 25% contribution, the federal government would put $5 billion into a $20-billion plan and the provinces would come up with the balance necessary to get themselves to $15 billion and you'd be there.
In reality, I think the PBO report underestimates the copayment revenue that would be possible. An extraordinary share of the prescription volume in the PBO report was exempt from copayments because people were over 65. Not all, but many people over 65 could afford that $5 prescription, which might have been a source of revenue, particularly for discretionary treatments that aren't about prevention and keeping people out of hospitals.
The maximum would be somewhere in the neighbourhood of $5 billion to run a fairly comprehensive program. Evidence from other countries, from the USVA and the New Zealand PHARMAC system, shows that they do go ahead and budget based on a conservative estimate like the PBO's, because they know they're going to live within the budget initially. What that will do is actually embed the ability for that system to sustain cost pressures, at least for the first several years, because they'll be able to garner savings from older medicines over time, which will allow them to bring newer medicines into the program at pretty close to a constant budget.