I asked a question on superuser that led to two answers.
Kamil Maciorowski's seems to be a good practical answer to my question.
However dirkt's answer gave me a lot of context, interesting links and made me learn quite a lot.
You could always offer another bounty on the question after the existing bounty is finished.
In this case the minimum rep you can award would be doubled up to 100, so you should be sure that you believe the answer merits it, but I have seen bounties used on several occasions to reward exemplary answers.
Additionally, if you offer multiple bounties on the same question, the minimum spend doubles with each subsequent bounty (50 reputation on the first bounty, 100 reputation on the second, 200 on the third, and so on).
In fact as you go through the process to start a bounty one of the options is
Reward existing answer
One or more of the answers is exemplary and worthy of an additional bounty