Late-2014 Macbook Pro - Fast SSD and 16GB RAM
These older Macbook Pro machines are very powerful, and available for around $1050 on Amazon, used.
https://www.amazon.com/gp/product/B0096VD85I/ref=od_aui_detailpages00?ie=UTF8&psc=1
I will simply say, I purchased on last month, and am very glad I did! It is a very powerful machine and capable of any task in the crypto world you might try to throw at it (like building out a complex blockchain such as BTC or ETH).
This machine comes with 16GB of memory, so it's also great for running Windows on, in either VMware Fusion, or Parallels.