RE: Best deer rifle under $600
Depending on where and what terrain you will be hunting, I will take a Marlin 30/30 for an "inexpensive" deer rifle. I have personally gone back to my 22 year old Marlin and have taken a 120 class 10 point and 2 does this season. My youngest son has been using the same gun and has taken a nice 8 point and a doe. All deer have fallen within sight of where they were hit, and 3 were neck shots and never took a step. We are hunting a place that is THICK and shots are under 100 yards (most are under 50 yards).
I would also seriously consider a T/C Encore. With it, you can pick a caliber to fit your needs. I have one in 300 WSM, and my son has one in 270. Both perform flawlessly.