If you need a Pegasos class desktop computer, try to find a second hand Pegasos 2 G4.

If you think the Efika will be enough for your MorphOS needs (chances are it will be, depends on what you will do with it), then go for that one instead.

All motherboards (even the Pegasos) needs peripherals like a case, gfx card, hdd, psu, etc. If you want it real cheap you can always buy a $99 board and put it bare on the desk, plug in a used PSU and graphics card from another computer (doesn't everyone have this kind of stuff lying around? ), *or* you could go for the option that has case, PSU, GFX, HDD etc included already.