Why do you take this so personally?  Why do you 
think that because you're a huge fan of one 
series, that entitles you to good deals on cels?  
I love Cowboy Bebop, Utena, and Five Star Stories, 
but it doesn't pain me terribly that I can't 
afford cels from those series.  It's superficially 
lame that one of the series I collect is 
increasing in price because it's increasing in 
popularity, but there's nothing I can do about 
that; no point in crying over basic supply and 
demand.  

Do you think it works any differently in any other  
collectibles market?  Cels are commodities, just 
pieces of plastic with no inherent value other 
than what someone is willing to pay.  Sometimes 
the buyer really wants the item; sometimes the 
buyer's just another reseller.  It's the same 
thing if you collect cels, if you collect Barbies, 
Fiesta Ware, Civil War memoriabilia, etc.  And who 
knows?  Antiques/collectibles markets crash, 
too--perhaps that person who's buying that cel 
with the hopes of reselling it for big bucks won't 
be able to do so.  

The only thing you really can do is set your own 
price limit, know what you're willing to pay for 
whatever, and don't sweat the rest.  It's not 
worth taking personally, and it's not worth 
constantly whining about how so and so is getting 
too popular and the "real fans" are getting priced 
out.  (Who's to say the guy in line behind you 
isn't a bigger fan?)  Too popular?  Eh, hey, time 
to find a new series, or maybe cash in your old 
ones, take advantage of market conditions.  It's 
just how the trade works, and you can take it or 
leave it as it comes.