Well, I don't like Tenchi in Tokyo, and only own 
3 cels from it, but you could find decent ones 
for around $20-30. At some cel shops in 
Shibuya, you could find some for 500-1000Y, 
and a lot were sold in bulk. I don't think I ever 
saw one over $100.

P.S. For anyone interested, I'm updating my 
site tonight. Weekly updates, baby!