Cheap barbells are not only more likely to bend (and you should be wary of any barbell that you dropped on your safety bars from a good distance with any amount of weight), they are also more likely to have manufacturing defects such as the bearings seizing or end caps coming off.
If you just bench, squat, deadlift, overhead press -> you are probably fine with a modestly priced barbell. I would still avoid anything with a bad rep for mechanical failures like the plague. Is your health and well being worth saving $50 to $100? Mine isn't.
If you do any type of olympic lifting such as clean or snatch -> you want to get a decent bar.
Knurling will be a matter of personal preference.
I picked up my bar from Rep Fitness and paid a bit more than the cheapo bars because I do incorporate some oly lifts.