For most anything I'd say around $4k is about as high as I'd want to go before feeling silly. The vast majority of my small pile of guitars didn't cost anything close to that much.
However, I will say that in one instance, I been looking for a great Les Paul Custom for the better part of a decade, hell maybe longer, but compared to what I'm used to, just about every single one of them I played had acoustic resonance with so much honk that they all sounded like a goose. I must've just been unlucky. Anyway I finally found one specific ebony LPC in a roomful of like 10 other ebony LPCs, and yeah this one had healthy Les Paul mids but minimal if any honk at all, and it also had a lot of treble snap I'm not used to hearing from them. Sounded incredible. I paid north of $6k for that one and honestly I did feel silly about it, but it also felt like a one-time unicorn thing I'd always regret not buying even though it was that expensive. It would've haunted my dreams and always been the one that got away. But I doubt I would pay anywhere near that much for a guitar again.