You have a tough situation but... I have a cheaper solution for you. Remember these are dogs. They inherently want to please you. You just have to let them know this.
First, get a squirt bottle of water and add 1 cup of listerine to 2 cups water. put it on a stream spray. DONT LET THEM SEE THE BOTTLE. Now this will take alot of your time.. you must follow through. Put the dogs in a place where you can be within accurate spray distance. as soon as they start to chew the collar, use a command voice. No. "NO" . IF you dont have a command voice then this will be usless. Learn how to have a command voice.. GOOGLE It if your unsure. Everyone has one, they sometimes need practice. Back to the chewing collar issue. When the dogs hear you say NO, and they do Not stop. you sneakily spray them on the snout. It will get in their eye but it will not cause damage. it is an IRRITATION. I have tried it on my own eyes and it sucks but it will get the dogs attention.
then after you apply the correction, love them up, and let them go back to the play, AS SOON AS ONE Starts to chew the collar again, you SAY COMMAND VOICE NO!! and repeat the spray.
SOON they will GET the message.. This might take all night.. or might just take an hour. IF YOU ARE NOT CONSISTANT In the training.. then don't even start. The dogs will not be benefited by inconsistant training.
HAppy training.
I have trained security dogs to not go after cats with this method.. it works.
Jack