SAG Ultra Low rates are $100 a day. There are, however, some hidden costs. The most notable being that technically that is for an 8 hour day. The final four hours of a standard 12 hour day are calculated at time and a half, which means $175 for a day. SAG also expects you to be fully payrolled. Meaning they expect you to pay for Unemployment Insurance and taxes etc. When you're shooting for only 25,000 these are significant additions. My go-to accounting guys charge a minimum of $700 for payroll services for a feature. That said, I don't know what the understanding at SAG is, but I've made several ULB shows that did $100 for a 12 hour day without doing payroll expenses. I think for the smaller films SAG often looks the other way, and figure that as long as none of the actors are complaining they'll let it lie... but don't take my word for it.
Updated rates: In 2015 SAG raised the rates of the SAGIndie contracts to: Ultra Low Budget: $125; Low Budget Modified: $335 daily or $1,166 weekly; Low Budget $630 daily or $2,190 weekly.