Bitcoin doesn't have a security budget, it has a marketplace for transaction processing and settlement.
To find the answer to "will bitcoin be secure in the future," think through the following questions:
is the processing and settlement market working today? Why?
Will the same amount or more people be using bitcoin in the future?
TANSTAASB
Also: Do people need the ability to send hundreds of billions of dollars of value (measured in current US dollars) across borders within 1 hour, with final settlement?
If the answer is yes, the next obvious question is: How much liquidity does that require?
The rest falls in place easily. Simply hold Bitcoin and sleep soundly.
