But are there ones that top over even Miyazaki 
cels?

Yep.  Five Star Stories.  Single OAV/film based on 
the popular manga, animated in the late 80s/early 
90s and subsequently disowned by its creator, which 
is to say it's long out of print and chances of it 
getting outside of Japan in a legit format are 
about nil.  LDs of this one can top $1k. Chara 
designs by Nobuteru Yuki.  Cel prices for this can 
reach well into the thousands for a good one; Anime 
World Star recently had three separate A-level 
backgrounded shots of some of the main characters 
for which they were asking 300,000 yen each.  I 
think the cheapest I've ever seen a cel from this 
is $499.

Other big-ticket anime:
Lodoss OAV (good shots of the main characters 
usually go for over $1200)
Sakura Wars (OAV cels from this of the main 
character will run anywhere from $500 up; I don't 
even want to think of how much video game cels, if 
they're out there, would run)
Evangelion (enormously popular show   no cels in 
general release = $$$, esp. for good shots of the 
major characters)
Older Tezuka productions, such as the original 
Astro Boy


BTW, even within Miyazaki/Ghibli material there's a 
huge price variation.  You can get cels from, say, 
Castle of Cagliostro for relatively reasonable 
prices, but anything from Mononoke Hime (from which 
cels were not released) is gonna set you back some 
big big bucks.