Hardware for Operating System development
Use a normal PC.  These come with x86 processors and all the other hardware and are exactly the kind of platforms that benefit from operating systems.  Even a old junker PC would be fine for this.  You develop on a regular PC running a real operating system and test on the klunker.  The other advantage to this is that it's free.  Surely you have some old PC or motherboard sitting around in some dusty corner, or know someone who does that has gotten around to tossing it out yet.