Why have rams become so expensive?

You pretty much answered your own question there. There are many variety of Rams, some are more expensive than others. The German Blue has been around for a long time and usually sells for less, the Electric Blue is a newer variety that has a more "neon" coloration than the German and sells for more. This isn't unusual for fish, as many species (Guppies, Angelfish, Discus, etc) come in different varieties with different prices.