Hmmm... as a complete system you should probably get somewhere between £300 and £400 I think
as parts: (all prices approximates)
Blizzard PPC Board 68040 25Mhz/PPC 603e 160Mhz and 144 MB Ram - £150-£200
Blizzard Vision GFX card - £75
Scan Doubler - £30-£50
and all the below wouldn't really be worth selling seperately in my opinion:
PCMCIA Right angle connector
Ethernet Adapter
High Speed serial card (connects to the clock port)
IDEFix 4 port adapter
OS3.9 installed with CD
Hard drive - 6GB if I remember correctly!
24x CDROM drive
So overall, I'd reccommend selling it as a complete system. You may get a little bit more cash for it as parts, but not much. Plus you may be left with all sorts of random bits...
Although, if you take it out of the tower, all the innards will fit in a static proof bag at the bottom of a suitcase quite nicely :p