for $100 you may be able to swing a boss ns2, but in terms of pure noise gate goodness, the isp decimator is the king

you'll have to stretch your budget a lil bit to get it though
if you love bbe products join the "i heart bbe" group. kthnx (click link below)

Quote by Dempsey68
get a cheap marshall... my MG15DFX has a button that simulates the sound of one of the expensive tube marshall amps.
ISP Decimator, but it's a little over 100.

The Boss NS-2 is pretty good, under your budget, but it's not super tight. Not bad, but not amazing.

EDIT: ^ Yeah buddy, you know what's up!
Dean MS STD V w/ Dimebucker
Dean ML '79
Jackson DKMGT
Randall RG75
Peavey Bandit 112
Boss NS-2