Why not just use virtual machines to sub out the RPis? Without the curriculum, it's not clear what they're trying to teach here. Assembly? Networking? Administration of the RPis?
Do we assume that 18+ folks are only interested in parallel programming if it's assembled of shiny pipes?
This. The first step to teaching anyone anything is to grab their attention. Especially kids/teens.
But I'll admit, the price is too steep. They can definitely do better
We had an overpriced external hard drive we had to slot into computers to play around with, but it helped because it wasn't a virtual "imaginary" thing.