Hmmm. Off topic, if I bought the Dujur formula, I'd breed more than one of them. =D For farming. Not too bad for battles, either. 500 gems a dragon is still steep, though. As it is, the only formula I've bought is for the Queen Dragon. Can't speak for the collectors, though. It's nice to have dragons that aren't common and are interesting.
However, back on topic Deus Vault was taken off for a reason -- that most people don't want to pay in gems for breeding formula, exclusive as it may be.