Cels Forum

Here is my situation.  I would like to start collecting cells of some of my favorite anime. These being Ranma, Gundam Wing, Tenchi, Lodouss, and a few others.  I would also like a cel of Grave of the Fireflies, but I am told that this would be a major undertaking.
My question is how much should a cel of one of these cost around?   I had a nice Ranma cell that I got for $55 but I gave it to a friend for his birthday.  
Also, I keep hearing about how you have to get to the sites right after they update, but how do you know when they do that?  Is there a mailing list that I can get on? 
Any help is appreacated.

   Thanks, 
      Thomas J.