Once he gets his DM Cert if he wants to continue to help with class he must purchase his own.
Let me see if I get this right.
You want me to be a billboard for your company, and provide promotion for the products you sell. That's reasonable.
You want me to do that for free. Well, that's not too horrible I guess, especially if I like doing it (diving) anyway.
You want me to pay to be your billboard?
You're nuts.
This is why I'll never do my DM or Instructor ratings - there's no reason to. The way I see it, if you want me to work for you and advertise your product, you can provide me with the gear you want me to advertise - at no cost to me - to use in that endeavor.
I'll leave the gear at the shop (that is, its yours and not mine), but I expect you to provide it, to hold title to it, and if there's a problem with it during my use in my professional capacity, I also expect you to fix or replace it.
I don't expect you to give me gear to use for MY OWN recreational diving; that's my problem. But I do expect that while I'm on your clock, acting as a walking (or swimming) billboard for your company, that you will provide the materials you wish me to advertise.
Anything less is purely outrageous.
Yes, I know the "you have to buy a kit from us that is of the gear we sell and represent" game is common. Its still outright thievery, and anyone who agrees IMHO needs to have their head examined, and I'm not talking about their hood side either.