I would suggest using WordPress click here . They have a large selection of themes to choose from. If you are looking to edit the themes there will be small fees involved. I am not entirely sure as to how much this will cost as I do not use WordPress to host my blog, I host my WordPress blog myself.
That is another route you could take, buy a domain and web hosting and setup a blog on the web hosting.
What I would suggest is go to WordPress.com and setup an account and play around with it and see what you think about it. There are other blogging platforms such as MoveableType and TypePad however these cost although another free alternative is Blogger click here . I have never had experience with Blogger so I can't comment on that but I would strongly recommend WordPress.
If there is anything else you would like to know about WordPress just let me know and I will try and help as much as I can.
By the way, it seems like your trip is for a great cause. Good luck with it :-).