I don't know what good levels are. Maybe think of it in terms of % of salary for the median employee? $30 wouldn't feel genuine to anybody, especially if it looks like people at the top aren't cutting back. $250 for a developer making $175,000/year makes a much smaller difference than for support staff earning $40,000/year.

Another thing to consider - if things are tight and you don't already have a holiday bonus, a certificate to get a ham, turkey, or meat and cheese tray at a nearby grocery store would seem more genuine than a piddly $30 cash bonus. Of course switching from ~250/year bonus to a ham will be a morale killer.