I used food-grade (can't be pool-grade) Diatomaceous Earth first, and it was working, but then we thought Pearl was pregnant. I didn't want the babies to be born breathing in a cloud of DE, so I tried the ivermectin.
What I got was Jeffers Ivermectin Paste 1.87%, oral for horses. I got it at the feed store for $5.99.
I squeezed a pea-sized amount onto the end of a popsicle stick, and then quickly smeared it onto the rabbit's lips. It seems they don't like having stuff on their lips, but can't do much about it with their paws, so they have to lick it off.
With Pearl, I had to get Ilovebunnies to get her into as much of a bunny trance as possible, then did a lightning-quick smear onto her lips.
One application for each bunny, then again 10 days later. If you suspect they are not eliminated 10 days after that, then a third and final dose. I did end up doing the third dose. You just have to be very cautious when you are dispensing it, that you do remember how small a pea is! The contents of the tube treat a horse up to 1,250 pounds, so you sure don't need much for a bunny!
The ivermectin is cheap, easy, quick, and not very labor-intensive, but you must be super careful. The DE is pricier, messy, takes more time, and labor-intensive, but is harmless. The DE has to be applied for a longer period of time. So it's just a matter of preference.