I LOVE TO TALK.
I give presentations sometimes for money and sometimes for free, if it's a good cause. (Good causes would generally be only educationally-oriented, non-profit, and non-revenue-producing events.) Please contact me to discuss either one at steveduncan99 at gmail dot com.
I'm generally found either in NYC or the Washington, DC metro area these days; if your event or venue is not in one of those two places, I would probably ask you to pay for travel & lodging regardless of how good a cause it is.
I would love to come give a presentation to your high-school, college, or grad-school class or non-profit organization (at least in the NYC or Washington DC areas) if you have a budget to pay me my preferred rate of $400; if your budget or available honorarium is less than that, I would still love to, but I can't promise, so please contact me to discuss. This also applies to walking tours for your class or group-- my walking tours do NOT actually go underground, but instead we peer into the urban underground (and into the past) by examining surface clues, looking down manholes, and tracing the routes of old pre-urban waterways in their path through contemporary sewer systems. These tours are a great way to teach students about how wastewater and urban hydrological systems work in today's cities. I sometimes even call them "sewer tours," because I like to focus on how sewers actually work, although most of my tours actually follow the historic routes or pre-urban streams or waterways so that we can examine how these landscapes have changed over time. You can also contact the wonderful folks at NYC h2o about tours or class presentations; I give most of my walking tours and education presentations through them, and they are often much better about replying promptly to emails than I am.
In general, for conference keynote presentations and similar, my asking price is $1,500-$2,500, plus travel and accommodation costs. (For per-diems and accommodation rates I go by GSA rates in the US, or State Department rates outside of the US. My preference is to stay over for at least one day when the location requires flying or significant travel.)
SLIDESHOW Presentations for classes, non-profits, etc:
$400 (or less, depending on your budget, though I probably shouldn't admit it.)
$400 (My existing tours are only in NYC and oriented around urban hydrology and history, but I'm always willing to talk about something new)
Conference Keynotes, etc:
$1,500-$2,500 plus travel. (This is for a presentation with visuals, customized for your event, generally running about 45 minutes long, but adjusted to your needs. Rate depends on the size of group, with some allowances for whether your organization is composed more of well-funded corporations versus impoverished academics/ adventurers/ etc. For shorter 15-20 minute TED-style presentations at your event or conference, please contact me to discuss individually.)