The UN suggest at least 20% of any transport budget with the following considerations
Introduce a national or city non-motorised user (NMT) policy if you don’t have one. If you do have a policy do you need to revise it?
Set aside at least 20% of the total transport budget to fund NMT programmes at national and city level. Measure the measurable goals, then collect the data you need and evaluate your success.
Ask users where they walk or ride and what they need. Pay particular attention to more vulnerable users, such as women, children, elderly people and people with mobility challenges.
Have the "political will" to make change, actively championing cycling and walking as modes of equal status to private cars.
We have a long way to go. I think we spend about 1%