Speaking just from my experience as a bar league shooter......
When I first started out, I was using a 15 oz bar cue. I liked the lighter cue because it allowed me to have more finesse. When I bought my own cue, I chose a Viking that was 18 oz. Most commonly, when you buy a production cue, 18 oz. is the lowest weight they offer. Now that I've been shooting for a little more than 2 years, I've found that a little heavier cue feels a little better to me (about 19 oz.). Weights of the cues are all about personal feel, but if you're comfortable with an 18 oz cue now, then I'd stick with that. Unless the cue you use now is just a bar cue. If that is the case, then a two piece cue might feel totally different. The balance points are so much different between cues. I remember when I first got my Viking, the feel was totally different from a bar cue, but it was so much better. As far as length of a cue, I believe 58" is about the standard length for a production cue. You dont need to go crazy with cost. Most generally, the higher the cost, the fancier the cue looks... But that does not necessarily mean that it will be a better playing cue. There are plenty of players cues that are available for under $100.00 that are actually pretty decent cues, in my opinion. Cues in the $100-$200 range are a bit nicer but what you spend is totally up to you. I wouldn't think that you'd really need to spend more than $300 on a cue unless you're really serious into shooting pool. Something else worth considering when purchasing a cue is a Warranty. McDermott and Viking, as well as some others, warranty their cues. McDermott has the best warranty of any production cue manufacturer that I know of and they are really nice cues. As far as the tip goes on your cue, a standard LePro should be just fine. But if you want to spend a little extra, you could go with a wide variety of tips. There is no such thing as "the best tip." It all comes down to what feels good for you. Most commonly, people use a 13 mm tip. I myself, like about a 12 mm tip, but some people think that the smaller tips make it more difficult to shoot with because they tend to put more english on the cueball than necessary. Again, it's all about personal preference. I think most people prefer a pro-tapered shaft as well. I like something with, at the very least, a 10 inch pro-taper. In case you dont know what the pro taper is.... The diameter of the shaft stays the same from the tip all the way back to the dimension specified (10", 14", 15", etc..), then it tapers out to the diameter at the joint. The alternative to the pro-taper, I believe, is the "European taper." The diameter tapers evenly from the tip to the joint. I find that shooting with one of these tapers makes it difficult because the shaft seems to bind in my bridge hand when I stroke the cue. Something that I was careful of when first choosing a cue was the pin. Vikings have a quick release pin, which makes it nice for quick assembly and dissassembly, but not so nice for purchasing a new shaft. Lucasis have a Uniloc joint, which makes it very quick to assemble and dissassemble and the joints are pretty common in replacement shafts, though a little pricier. A 5/16"-18 pin is quite common for many different cues and you can find tons of replacement shafts readily available, so choosing a cue with a 5/16"-18 pin might be a nice thought if you plan to try out different shafts. I think that about covers most everything you should consider when looking for a new cue. As far as places to buy.....
Pool Cues, Pool Cue Cases, Billiards and Gameroom Accessories at PoolDawg,
Pool Cue - Pool Stick - Billiard Supply - Billiard Cue - Cue Stick - Pool Cues - Pool Sticks - Billiard Cues - Cue Sticks,
Pool Cues, Predator Cues, Pool Cue Cases, Billiard Supplies Store, Break Cues & Pool Sticks, and about 10 million other places... But don't overlook ebay. I've found some really good deals on ebay. There are a couple of sellers in particular that make cues that I like. Kccue makes some nice cues for very good prices. vegasbilliardman and deangelo1024 are good ones to check out as well. I've bought cues from these 3 sellers and have had good luck with each. There are also several ebay stores that have good deals on new cues. I hope all of this information helps
Geoff