Well, unlike Mr.Hanson, I would not suggest EXACTLY what size and weight to buy as not everyone likes heavy cues or large tips. A cue is an extension of your skill and should be custom to your tastes. The feel as it slides through your fingers and the size of the tip as you sight down the cue can have a major affect on your shot if you are not comfortable. I suggest you go to a cue dealer and try out a few different cues and different styles. some people prefer Irish linen rather than smooth or leather wrap. But I will agree that you should not spend more than 150$ on a new cue because as your skill and experience grows you will come to know how you play and the cue you buy today may not fit the profile you will want.
Normally for first time buyers I suggest a Viking or a Duffrin if you like the feel of wood but you have to be careful not to drop it or knock it against the table. If you are not very careful and you would rather a smooth finish I suggest a Cuetec. The Earl Strickland model is very popular and very robust. I've seen people get really angry and wack the table and not damage the cue in the least.
A lot of the price difference in cues is the wormanship and brand name. I assume that demand in a cue also plays a part in the price. Anything over a few hundred dolars and you are paying for the wormanship alone.
Jay