Approx £100 - £125 for the base unit assuming every thing works and it looks in good condition. This is a rough guess - based on MY opinion as to what it is worth - i.e. what I would pay for it. Others might pay more or less. the problem from your point of view is that there are some very cheap new base units up for grabs from many dealers at present. For not a lot more, you can buy new with a reasonable spec if you dont want a super-fast gaming machine.
Hope this helps. kp