Depends upon condition and model really. In the past I've bought do'er upper's for £40 (Mkii, Perfekt trigger) but needed to spend on springs / cocking lever etc. The 'S' goes for a bit more in the same nick because of the Rekord trigger. Good ones, £100 without glassware on.
NB: being the favourite of Boys Brigades and Scout troops be prepared for some seriously well worn samples second hand, especially if they are in numbers at an RFD.