We generally do the train, I think coaches might be tricky... train up to London Bridge (not the express, that will be more expensive) and then down to Folkestone, OR you can go via Redhill and Tonbridge - might be cheaper as you are avoiding London. There are not as many trains going that way, but it's not any slower.
This is part of my site The 'Gerald that I set up in a fury of enthusiasm when I first came to Folkestone sometime in '04. I'd been a frequent visitor for a few years previous to that but I am technically one of those Down From Londons you get nowadays. The site used to be updated more frequently with a calendar of events and voting for best venues and things, and I know it was a handy resource for others who were thinking of moving to the area. Now I've moved out of Folkestone again (though only a couple of miles) it doesn't get as much love as it used to. Ironic really as Folkestone itself is now becoming the exciting place we always thought it was about to become. I am not Gerald BTW, the name comes from a fake newspaper in an episode of Brasseye or something, the Portsmouth Gerald, + how there is a local paper here called the Folkestone Herald. Puns like this are GRATE aren't they? Do contact me if you have anything to offer, email anythign @ this domain, or try @folkestone or @pauly on Twitter.