What Saiyan said was correct; this is what I've learned so 
far:

Hand-painted, a hanken mono is expensive to produce as it 
is to buy - it should be *perfect* - and you'll likely only 
get your hands on one through a reputable dealer (or an 
individual collector, if you're lucky). Unlike normal cels,
hanken mono have their OWN copyright, like an individual 
painting from Money does, whereas it's the anime SERIES/film 
which is copyrighted in terms of normal cels. They also 
tend to be much bigger than a normal cel.. Hanken mono are 
the "holy grail" of cel collectors - no kidding.! Yah, I'd 
love to get my hands on one.... ;_; Now, it's true that they 
tend to be ungodly expensive, but keep in mind even not all 
hanken are "created equal." Imagine a Shin Tenchi hanken 
versus an OAV Lodoss Deedlit hanken. [shudder]