Soulstice, I feel your pain. Here’s a couple things to keep in mind…
Clark blew their own foam into molds. Yes, the molds were expensive, but very durable. All they bought was raw materials.
The only other processing was stringers.
Any EPS blank is going to touch two companies between raw materials & you. One mixes the chemicals & blows the foam, the second hotwires it or machines it & puts in stringers etc. They both have their own rent, overhead, and transportation between them. The second one also has waste material - even cutting multiple blanks from a big block, you get the extra wedges at nose & tail. Waste is, well, waste. And it costs something.
Two overheads (& fair markups) vs. one, extra transportation, waste…I’d say that could add up to 30% pretty easy.
The way around it is to just deal with the first one - buy the blocks from the primary manufacturer and hotwire them yourself. Probably save you 50% or more. Sure, there is some drama & hassle, and you have to come up with a bigger nut up front. But with the other factors in mind, at least its a decision you can analyze with clear information.