Tough one. Alot of people have them advertised at the prices that previously would have been snapped up in a minute and they have just sat there. $1,000-$1,250 seems to be a price you can get for a full kit with Mainboard, DS UltraBios Cart, full Simms and a blue scsi set up you don't mind waiting. Similarly a full original 3rd strike or JOJOs set with everything including boxes and art set could get you a bit more (maybe $1,500-$1,750 maybe thats on the high side) if you dont mind waiting. If it's literally just a motherboard maybe $600-750.
I am almost 100% sure there will be people out there that don't agree with these prices but if I was buying now, I would be looking to pay about 10%-15% less than what I have stated and there seems to be enough listed and enough listed for some time to hold your ground.
I am also interested in what others think.