Technical Advisor Salary (United States) http://www.payscale.com/research/US/Job=Technical_Advisor/Sa...
Technical Advisor Salaries https://www.glassdoor.com/Salaries/technical-advisor-salary-...
Advisor to a startup: 0.25% to 0.75% vesting over two years. Time commitment is in the 1 meeting a month to 1 meeting per quarter.
Take a look at this legal template: https://fi.co/contents/fast#
I've seen advisors taking a fixed stock option package and/or regular fees in exchange for being available. You'd be a technical advisor just like their lawyer is their legal advisor so I'd structure it like a retainer plus hourly cost. Aim high if they want to add you to their about-us page, investor presentation or press release (http://blog.mapjam.com/openstreetmap-founder-steve-coast-joi...)