Now we are close to one answer how much budget is enough to cover the technology investments.
- Buying a commodity? Choose the cheapest option.
- Pursuing an innovation? Invest proportionally to value that the tech initiative brings.
- Complex system, which is difficult to classify as a commodity or a strategic tool? Disintegrate into commodity subsystems and the rest, then apply above principles.
The example of a complex architecture disintegration given in NFV / SDN books on this site.