Try and find a unit close to you, and contact them. We started out as Union and then moved to a CSA unit. We still belong to both. Some units are more family oriented, and have families that all reenact together. Others are living history only.
I would say the easiest is to go to an event, look at the camps and then ask questions.
As far as expense, well, lets' just say this isn't a cheap hobby. You need the tent, and uniform or dress to start. My unit loans out equipment for the first 3 events. I have had very good luck selling my equipment on Ebay and moving on to better as I go. Used equipment can always be sold, which has helped us out a lot.
We all had to learn at first. Good luck, it's a great hobby.