According to this thread, Monotonite has only one use. It's an ingredient in making another, rarer and more valuable, component: the Quantum Particle.
You need a couple Quantum Particles to complete the Crown of the Thrice Great, and you need a LOT of Quantum Particles to complete any of the largest Legendary Backwings. So even with only one use, Monotonite is still a hot commodity.
As for "Alchemized", that term can just mean anything made via Alchemy, but if you're seeing it in an item's name, it's there to distinguish an Evolving Item that was alchemized from any of the ones that were bought from the Cash Shop. Think of it as just another kind of "generation" of EI. As for why it costs more, that's because it can be pretty costly to alchemize something as complex as an EI, and the crafter is just trying to get a return on their investment.