beginner question

To answer your question about computation power and mining - whoever is hosting a blockchain node that is participating in the blockchain network will need to pay for the compute power. If you deploy a smart contract on a blockchain network, but you do not host a node yourself, you don't need to directly pay for the compute power. 

For Workbench - the VMs that you see are running the microservices that are in the Workbench solution. Workbench currently is designed to work with a private Ethereum based blockchain network - this means that someone is hosting a blockchain network, which is NOT a public network. So, either you or someone else will need to host a private blockchain - the VMs that are running the private blockchain network will be doing the block creation. In terms of your cost concerns, you can pause the solution to save costs. 

Hope this helps!