You need to post up photos for a precise evaluation.
That said, is it just a GTEK or a 160R? Is the Rotor an R2? If not, what generation is it?
GTEK (the type with macroline) - approx £190 - £230
GTEK 160R (with air pipe) - approx £280 - £330, depending on what it comes with and what anno it is
Rotor - approx £40
R2 - approx £60
People are selling Spires & TFX's as low as £30 -£50 now, so it's really a buyer's market for loaders. It means that a Rotor may sell for the same.
Remember there is always some troll who will say your gear is worth less than what it actually is worth, probably because they have an eye on it themselves. Ignore what they say, unless you are very desperate for quick cash.
Also bear in mind when buying, say, an Eclipse marker that is advertised as a "one of one" because of the anno, check who did it - because aftermarket anno invalidates the warranty on Eclipse markers.