In the UK you'd be looking at between £2500 and £3500 depending on condition.
But the usual rule of sale applies. It's only worth what a buyer will give you for it, or conversely, what a seller will take for it.
A lot will depend on condition, has it been gigged, what extras come with it, and how old it is.
NEW ones can be had for £4000 (see below as an example) and with extras too, so a 2nd hand one might not be the best option when you weigh it all up.
https://www.achamilton.co.uk/Genos/GenosBundle2.htmAnother thing to consider is this. If you buy it 2nd hand from a dealership you'll usually get some kind of after sales support and guarantee. From a private buyer you will not generally get any.
Keith