Below a certain price point, choosing a 3 way setup instead of a 2 way setup starts to be more trouble than it's worth. You have to make such a compromise with driver quality to be able to buy 6 instead of 4 that I think that you'll end up worse off. That said, here's my $100 attempt:

Midbass: Dayton DC160-4, $24.63/ea
Midrange: Fountek FE85, $12.80/ea
Tweeter: Dayton ND16FA-6, $9.64/ea

This total comes in at $94.14 from Parts Express. If you have the room for a shieled 3" driver, you can substitute the Fountek for a Hivi B3N, which leaves you just enough money for a Dayton DA-175 7" woofer instead of the DC160. The DA-175 is an 8 ohm driver, but has great low end and good excursion. I actually use one as a subwoofer in my dining room.

I would probably sneak ever so slightly over the $100 limit ($102.04 to be exact) and use the Dayton DA-175, Fountek FE85 and Dayton ND16FA.