Well, I've owned 3 folders between $300 and $550, so I have fairly limited experienced. Here's what I've owned, and my opinion/experience of them.
1) Brian Tighe Mini Tighe Rod--Flips wonderfully on bearings, beautiful fluted blade. However, I am a large guy (6'4" 250lbs) with L/XL hands, and though I'm ok with most 3"~ bladed knives, the curvature of the handle made it difficult and uncomfortable to use. I probably would have been fine with the regular or large size. Otherwise, I really like his designs, and in the future may try another in a bigger size, straighter handle.
2) Strider SnG--Black lego, flamed Ti, S30V blade. Great ergos, well made, strong lock, no issues at all. Needed the money so I sold it, and deeply regret it.
3)Three Sisters Forge Beast--My favorite knife I own. The waterjet presentation scale gives excellent grip, and the ergos are perfect for my hands. Very smooth operation, and Jim is wonderful to deal with. The initial one I received developed blade play/lock issues, but I sent it into him, had it back in a week and it is absolute perfection. Sharpest blade I've ever received new or used, carved a pumpkin with no noticeable difference in sharpness. At your price range, a phenomenal deal.
My advice is to really look at customs with your spending limit. I've often looked at Sebenza and Umnums, and they just don't do anything for me. At their prices, I would rather have something custom/mid-tech.