May I be so bold as to conjecture that no knife, judged strictly on it's mechanical attributes and performance, is worth $100/blade-inch or more. When you get up to the really hardcore customs, I think the extra cost comes from the craftsmanship, artistic details and certainly the maker's name. If he's well-known and respected his mark will command a high dollar because the piece is expected to retain and grow in value based on his good reputation.
(It's the same with guitars, even comparing factory made ones. A Korean-made Epiphone will never be worth as much as a USA-made Gibson, even though they're literally made from the same blueprints and materials. Epiphones are a great value, very well-built. But with a Gibson you get somewhat better woods, much better pickups, F & F, etc... plus the Gibson name. It's been said that you can set a Les Paul on fire and let it burn till there's nothing left but the Gibson logo on the headstock... and it will still be worth a couple hundred bucks

) Don't even get me started on true custom guitars... you think knives get pricey?!?
If it's a user knife, I agree with Joe-dirt and Lenny_Goofoff, don't spend more than a couple hundred bucks. I doubt you'd see a real appreciable jump in performance till you got closer to the high end of price. However, if I could choose between two knives I liked at similar cost, one being a factory model and one being made from a respected up-and-coming maker, I would take the custom every time.
Because you're likely to get a lot more in the details, fit and finish, differential temper, etc. Plus it's just plain cool to have something custom-built

That may be worth an extra $50-100 to you, or you may decide to buy another factory knife instead.
There a couple of makers here who have been highly praised but whose knives are competitive, price-wise, with the high-end factory stuff. In a few years I'm sure their prices will climb as their demand and reputation does.
Sorry this is so long, get me yappin' about guitars and knives and I'll jabber all day if ya let me.