I have a marshall 2x12 8222 cab and was wondering if anyone has any idea of the value of one of these at the moment?

Much appreciated,
Why don't you just post that it is a Valve State cab? You may get lucky and get $100 for it, those cabs are pretty horrid.
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
GFS Greenie/Digitech Bad Monkey
Morley Bad Horsie 2
MXR Smart Gate