The cheaper ones arent really going to give you any better quality over the more expensive ones. At best, you may get additional channels. Digital TV works in this manner: Either you get the channel, or you dont. If youre somewhere in between the image will completely cut in and out.
That being said, i have a cheapo set of rabbit ears ($10 maybe) in the bedroom and we get almost 20 channels. Our cable tv subscription only gives us like 25 and half of those are free channels anyways. Of the free channels you get over the air (4, 6, 10, 28, etc...) most will look better on your rabbit ears than through a cable box. Cable providers take that same signal you get with your antenna then compress it before sending it down the pipe. That compressed image is of lesser quality then uncompressed signal you pick up with your antenna. Major broadcast companies are suing cable companies for doing this. There is the potential most free channels will become subscription channels if things don't work out right.
As soon as our contract is up we are cutting the cord and going rabbit ears/XBMC only.