Hi,
prices for heads vary quite a lot, I have bought several on their own in the past or complete engines.. For less than a head before. Is there any reason why there are no cams? If you want a reasonable price it should be complete..
IF there are no cams, does that also mean that there are no lifters? Are all the screws/bridges there?
I suppose for a complete head you could say from £40 - £100 in known working order depending if its trade or private, but as you said you also see them for £125 on places like ebay.. How badly your need or availability will usually dictate what you pay.
If its in bits and your probably not going to use it ever, give the guy a break/do a deal..you never know when someone will do the same for you in an hour of need
Just my 2 pence worth.