Inferno rubies are only so expensive because -everything else- that JC's cut is pretty much -not- needed at the moment. Nearly every gem slot on gear is -red- which means that there is no debate about what to socket. People use if we're lucky 2 non red gems for their meta activation and some dps metas don't even require that!

So yeah 250-300g is expensive per gem, unless you consider that every other gem is worthless ... so it just -seems- more expensive, where as if the price per gem were spread out more evenly amongst other colors it wouldn't seem that bad. It's just not, because the one gem people want -- has a lower drop rate than any other color which is in turn pretty much worthless. {Not all realms are the same there are a few orange gems worth anything and 1 purple one worth anything, but everything else is like 3-5g each. With the deposit from the ah taking their cut it's almost better profit to just vendor them all..}

So while I enjoy the raw stat boost on my gear + free set bonus for using my best gem, I feel like Blizzard really did JC's a disservice by making so many red gems on gear.