Keri,
I'm pretty sure others will have better methods for you but here's what I use for smaller cages:
1. Fold your cages flat. If they have a clear plastic vinyl side then try to fold this part inwards, so that the netting is on the outside. This doesn't matter too much but will help disinfect the cages more thoroughly.
2. Prepare a 5-10% bleach solution. 5% will most often be enough to get most things but 10% doesn't hurt especially if you're dealing with Oe. Prepare enough solution to cover your cages.
3. Soak your cages in the solution for 20 minutes.
4. Then remove, rinse, and dry.
I have heard Milton Solution will also do the trick. It simply takes a little longer to disinfect but I only use it for cleaning the lab floor and soaking host plant leaves. You can always experiment a little by microscope testing. Most of us Monarch breeders I am assuming have one to test for Oe?
All the best,
Josh