Well I have had luck finding at least one 
dream cel from a couple of the series that I 
collect heavily (DNA^2, Trigun, Detonator Orgun, 
Vampire Princess Miyu, BGC OVA, SMJ, Escaflowne 
(not up yet), Gunnm, Super Atragon (not up yet), 
Slayers, Tenchi Muyo, Hakkenden, Iria, Last 
Unicorn, Macross plus, Gundam X, Gundam wing, 
Nausicaa, Mysterious cities of gold, Silent 
mobius, and Voltron (not up yet)). OK. Looking at 
this list, I would say I wound a lot of them. Of 
course, some of these are from less popular 
shows (thank god their are more cels than 
collectors for detonator orgun, silent mobius and 
super atragon or else I would be really poor).

Overall, many I got lucky on and found them 
relatively cheaply, but some I had to trade quite 
a lot for or pay huge amounts. It really all 
depends on how popular the series is. My four top 
wish list cels that I have not found (Nausicaa 
while walking on the golden field, Nausicaa from 
the ending credits, Lina Inverse as LON, and 
Belldandy from the final sequence of the OVA) 
would all be insanely expensive to get, but I can 
still hope someday someone will offer one of them 
to me (if anyone has any of these three and wants 
to give them a new home, please drop me a line).

We can all dream.
Marcus