So 12 individual crystals was a cheaper solution than being able to tune into any of the 720 usable channels that the rest of the receiver unit is capable of?

No, not cheaper. It just wasn't invented yet. The old radios were all analog. Today they are mostly digital. They use just one quartz crystal and they mathematically change that one frequency to any number you need. These are called "frequency synthesisized" radios. Yes, they are way cheaper than all those custom cut crystals.