The Pico 5 Starter Kit is the most cost effective way to get into a true hardware cluster. It comes with everything you need to get started except the micro SD cards for storage and the Raspberry PI computer  boards themselves.

You can use this cluster to run almost any kind of distributed or parallel software. Run your own LAMP cluster, Docker, Kubernetes, Hadoop, ElasticSearch, Cassandra and many others. Also learn languages like Javascript, Java, Pthon, R, and so on. Use for Development, QA, DevOps, or Education.

The Pico 5 Starter Kit contains an 8-port 100meg Ethernet switch,  power, casing and all cabling. Each kit contains heat sinks for heat dissipation. Case panels are clear and covered by a paper/plastic covering for protection.

You need to supply your own Raspberry PI 2s or 3s and micro SD cards.