Options seem to be commonly offered as incentive. Depending on the stage of business your client is at, and depending on the nature of your advisement service (ie, marketing, financing, sales), you may not want the risk of the value of those options, and should have something different to counter. I have had advisors seek monthly stipends in addition to liquid equity, to some that just do it because they believe in my mission, have time on their hands, and want to help. I prefer the latter, but they're prized friendships and come with time.
But really, you may just as well look to your own needs, financially. What's your time worth? A wise man (named Wiseman, actually) once advised me for free (because I was marrying his daughter) as a gift. He said what I've actually adopted into a project planning tool, basically a form of Reverse Engineering. It would go like this: set your goal, and if it's financial (I've learned mine typically are not), set the date for your goal to be realized, then factor your living costs along the way, and account for a reasonable compounded savings/investment portfolio, and eventually divide the remainder by the number of hours you think are optimal to work in a given day/week/month/year, and there's your hourly rate. Of course, you also need to reconcile it with the going range of rates for a particular discipline, but you get the picture. If you're as good as it gets, charge what you want, but expect people to shop around too.
Let me know where you go.