Good scopes in that $400-600 price range would be the Vortex Venom, Viper HS-T, Strike Eagle, Arken SH4 Gen2, Athlon, Primary Arms, SWFA SS, and many others.
I have about 15 Vortex scopes, and recently just bought an Arken SH4 Gen2 6-24x50 MIL VPR scope, and I'm HIGHLY impressed so far. 2 different days at the range on my .260 Rem, and it's been perfect every time. Holds zero, and the zero-stop is the best I've ever used. Once you reset the turret to zero, and tighten it down, it's like it hits a solid wall when you return to zero. I think the zero-stop system on my Viper HST scopes is terrible. It works, just a bit of a pain in the ass to reset and adjust with the brass shims, removing the whole cap, etc... It's an ordeal. The Arken you unscrew 4 cap screws, reset to zero, tighten 3 cap screws, tighten down the zero stock, and then tighten the set-screw. Takes no time, and only requires a 2mm allen wrench.
I'm fixing to send off one of my old Viper HS scopes I've had for about 10 years now. It's got a lens coming loose, and when you rock the magnification ring side-to-side, you can watch the reticle wiggle with it. Not good. But, their lifetime warranty will take care of it. Maybe, since they don't make that scope anymore, they'll let me pay the difference and upgrade it to something better, like the new Strike Eagle 5-25x. Vortex is usually pretty cool about stuff like that.
That being said, I pulled that Viper HS off my new Christensen Arms Ranger 22, and put the Viper HS-T 6-24x50 that was on my .260 Rem (before I put the new Arken SH4 on it for testing), and now that HS-T will remain on the Ranger 22. I highly recommend it, as well.