The Centris 650 (or the slightly later Quadra 650) is one of the last machines of the era, but also cheap, expandable, and hackable. As a bonus, it’s capable of running the final version of A/UX.
(From: http://www.cy384.com/projects/centris-650.html)
This is the same developer that released the SSHeven SSH client for System 7/8/9 – I look forward to seeing what they come up with as upgrades/hacks for the Centris 650. The 650 is really a great machine, and I am so glad I have one of my own.