A book by Nunez, 1981, is sometimes cited for conductance of extracellular fluid:

P.L. Nunez

Electric Fields of the Brain: The Neurophysics of EEG

Oxford University Press, Oxford, UK (1981)

A quick online search shows the value cited from Nunez is 1.56 S/m = 64.1 Ohm cm.  Anther reference is Ranck, 1963 for rabbit CSF.

Thank you both for your answers. I had a look at these references and related studies and I finally found one that sounds pretty interesting (I've only read the abstract).

The electrical conductivity of human cerebrospinal fluid at body temperature. Baumann et al. 1997

They measured the conductivity of Human CSF at room temperature and body temperature. What seems interesting is that CSF conductivity at body temperature (1.79 S/m ) is higher than the commonly used value (1.43 S/m).

Thank you again for your help.

I suppose one can extrapolate CSF figures to perilymph on the basis of chemical composition

Hear Res. 1999 Mar;129(1-2):1-6.

Sodium, potassium, chloride and calcium concentrations measured in pigeon perilymph and endolymph.

Sauer G1, Richter CP, Klinke R.