If you want to get experience of working with higher node counts without breaking the bank, people do case kits for raspberri pies so you can build your own cluster.

For actual computing a modern higher end processor/server will murder it but its' closer to the real world of clusters than anything (so much so that there is a company that does 100+ pi node clusters for super computing labs to test on, you can't obviously run scientific workloads but it's cheaper than using the real machine as well).

https://www.zdnet.com/article/raspberry-pi-supercomputer-los...