Why do Solid State Relays cost so much?
Principally, you're paying for the testing. UL and CE testing is Very expensive. Also, lifetime and reliability testing (the crydom relays are specced to 100,000 cycles), which means that crydom has actually run a number of the devices through 100,000 cycles at load.

Furthermore, you're also paying for liability insurance. If an appliance fails and kills someone, and the only AC-facing component was a crydom relay, it's crydom's problem. If the AC components are your own, it's your problem.

Lastly, while it's true that a discrete relay solution is preferable in large volumes, you often see SSRs in small-volume or specialty products, where assembly and testing costs dominate the expenses, rather than raw component costs.