Under $100 for a very nice gi could be a bit tough.
That being said, if having the top-of-the-line is not what you're going for, $100 will easily get you a very decent gi.
My recommendations for under $100:
Sirius (might be right on the edge of $100).
Fuji is good, though not excellent. Great for the money. HCK is very good, though I don't personaly care for the cut of the gi. If you have long limbs, probably not the gi for you.
Padilla&Sons I have no personal experience with, but have heard good things and their prices are nice. (MatRat Martial Arts Kimonos and Training Supplies
I have heard almost universally good reviews from Sirius. The prices are good, though not insanely cheap. If I had some money to throw away, it would probably go to them.
If you're in the market for an exotic gi, GroundForce makes a hemp gi that runs about $100 including shipping. I have one, it's fairly lightweight, the fit isn't perfect. But, to each his own.
Hope that helps.