i use co2 its very simple and effective.... i have a giant sterilite tub i use as a chamber.. i purchased and 5 lb co2 for cheap online and a shop nearby refills it for me for about 25 a pop. I use it all the time as I have a breeding operation and I get more than a few weeks of use out of it each time before i need to refill it.. I purchased a small hose that goes from the tank right to the lid of the sterilite so the co2 flows in from the top.... turn on the co2 at a very slow setting as to not freak the rodents out and let it run for about 15 seconds.... off it goes... and just wait..... its very efficient .... i would highly recommend it.
i have used dry ice in the past but i found it was costing me a lot more to do it that way
cheers