Dave Cornthwaite is good. At 27, he packed in his couch potato existence and is in the process of completing 25 1k journeys using non-motorised transport. So far he's skateboarded across Australia (3600 miles), kayaked 1500miles, SUP'd the Mississipi and tandem biked across America. He's an inspirational character and a good laugh. He's written a few books and does talks, much of it going to charity.
Even better is another speaker I saw, Alan Chambers MBE. This man is seriously impressive and will hold a crowd mesmerised for the duration of his talk and for a long time after too. He spent five years planning the first unsupported team to reach the North Pole from Canada, only two of the original five made it, but what a tale he tells! He received an MBE from the Queen after this expedition. I'm surprised Hollywood hasn't bought the film rights as it'd make a great film.
David should be cheap enough, but I'd imagine Alan would be a bit on the pricey side. Just guessing though! I'd pay £10 to hear Alan again but interested in hearing anyone you get. Whereabouts are you based?
Links:
http://www.alan-chambers.com/
http://www.davecornthwaite.com/