You've actually got lots of options with $100, but your best bet for a new pipe will probably be Peterson, Stanwell and Savinelli as stated above if you want to remain within the realm of well known and reputable brand name pipes.
My preference would be for a Stanwell out of those three, but it's basically a toss up, more or less. Some would disagree..in fact I would disagree, but for the sake of avoiding argument I'll call it a draw between the three.
You could maybe get two of the above mentioned brands as estates, for the price you could pay for one of them new. Might take some patience and alot of ebay and/or forum trading post research, but would likely be worth it in the end.
If you are super duper patient and dilligent, you can very occasionally find a deal on an even higher grade pipe than your run of the mill stan, pete, or sav.
There are a couple of very good carvers who could make you a pipe for maybe $150 or so. I know when the budget is tight that extra $50 can really be hard to find, but it's worth it to my mind to get a "custom made" pipe, essentially designed and carved specifically for you.
The guys in the factories may not have the end user's satisfaction in mind at every step along the pipemaking process. whereas the guy who knows your name and has his reputation on the line has a little more incentive to put the best pipe he can in your hands and do what he can to make sure you are happy with it.