You should post over here too. http://www.jeepforum.com/forum/f325/
Taking something like this to a shop without doing the preliminary work yourself is an invitation to a huge ripoff. There's a big difference in telling a shop "do this and weld that" compared to "what do you advise?" Not everyone has the time, tools, skills or workspace to do a frame repair but either way knowledge is your friend. Also, if it's really bad don't be afraid to swap the whole frame.
YJ frames generally rust in about three places; at the rear shackles, around the steering box and at the skid plate and to a lesser extent at the rear shock mounts.
Here's a couple threads to get you started