That would have to be a personal thing.  Each 
dealer/person has to figure out how much is 
enough.  Because as the cel works its way around 
each person get something from it.  In my opinion 
enough is what ever you can get someone to by it 
at.  

I had to deal with this situation a few times 
someone gets to the cel before and I have to buy 
it from them.  I got the cel and if I see one 
cheap in the same sequence for less (its happened 
to me to). I'm still not disappointed because I 
didn't get the cel because of the price.  I got 
the cel because I wanted it.  

Also as other people have pointed out its all in 
the market.  The one thing that is unique to cels 
is that there is no true guide that I know of for 
cels(correct me if I'm wrong).  You can't get a 
beckket, overstreet, wizard guide for cel 
prices.  So you can figure out what is a good 
price.  Therefore people can charge whatever they 
want and sometimes get it.  That I think is a 
shame though (not having a guide that is).