I think, for me personally, the biggest sacrifice that is made with cheaper cues is the weight distribution / balance of the butt. Cheap cues generally don't get this quite right and you never get the feeling of the cue floating in the hand. I think the cheapest cues I've tried that had good balance was a low end McDermott G-series. But even some McDermott cues have weight distribution issues, especially older ones. Occationally you get lucky with a cheap cue, but usually they feel unbalanced compared to expensive and well made cues.
Obviously the cheaper cues generally do not hit very solidly, but generally you get used to it and it doesn't really impact the game much. The cueball still does all the work it needs to. In the end, the cue is a stick with some leather stuck onto it. With todays technology and knowhow, it's really hard to mess up something so simple.
The appearance of the cue is a matter of taste and personal preference and may not be important at all to some people.
I would warn against some of the cheaper China made cues. I bought a 40 dollar McDermott Lucky cue and after two break shots major glue joints started failing inside the butt. The cue is now useless as it makes a terrible noise and the feel is completely ruined, even though it is straight. I reglued some of the failed spots (for instance the joint collar), but can't do anything about the insides. Thinking of cutting it up and making it a jump cue.