It's exactly why I rarely use it any more. I have had one 125ml bottle here for nearly two months; wouldn't have last me three days under the old regime!
I agree with Shambles. 1.5mls is my starting dose, and my tolerance hardly ever moves, and I tend to use small doses frequently. 1ml per two hours at night time will keep me going back to sleep. I take it more frequently, during the day. Maybe 0.5-1ml per hour, and that sends me nodding a lot. It is a strange one.
I wouldn't bother going any lower, to be honest i don't think you'd get anything worthwhile out of less than 1 but it's always safer to test with a low dose first.