It’s one of those ‘it’s worth how much someone is going to pay for it’ questions. The K12 seems to get some very good praise in terms of the trigger, but in the UK people tend to avoid them because of the lack of clear technical support. It also depends on condition and model (I think they all have the absorber in?) - and whilst being a lefty is something people will hunt for, this can be easily remedied by purchasing a right hand grip.
The cheapest I can find for a new one is £1500 ish, so I would think it would be worth around 800-900 depending on age and the age of the cylinders ? Only ever borrowed a k12 for a quick play, very nice to shoot.
Best
Doc
Please tear carefully along the perforation.