I won't argue with you for a moment that safety equipment is expensive. $500 or $600 when you are racing on a tight budget is no doubt daunting.
Your club members have a choice to join USAC or join QMA or stay as an independent. Making the choice to join one of the national sanctioning bodies will come with a responsibility to follow a set of rules; including the use of certain pieces of safety equipment.
Your argument that "other tracks race without the equipment" or that "we raced for ever without this equipment" just doesn't sit well with me. NASCAR drivers used to race with shoulder belts, open face helmets, no head and neck restraints, but that has all changed. Why? Unfortunately, many of the changes that have taken place at the professional level are the result of tragedy. Do you want to wait for a tragedy to make a change. The fact of the matter is that everytime we strap our kids into these cars we are putting them into a high risk situation. You can't deny that. They go fast, they crash hard, they have a tendency to flip, they have gasoline engines and fuel tanks, etc. There is always the risk of fire, of broken bones, of a head/neck injury... The tools to keep our kids safe are available. You just have to use them.
If I were in your position; First, I would do everything in my power to ensure that my kids had the safety equipment required by the sanctioning bodies. Then, I would put together a presentation to the club talking about safety. I would talk about the risk of fire. I would tell the story of the young girl and her family that never thought a fire would happen in her racecar until... Once I had established a strong case for the importance of proper safety equipment I would open the floor to the members for ideas about what we could do to ensure that every club member, no matter their financial situation, could have the equipment needed to keep them safe. Can we hold a fundraiser(s), car washes, bake sales, candy bar sales? Can we get donations/discounts from equipment manufacturers? Can we contact local race team owners for support, donation of used equipment? Can we put together a profile about the club, the fun we have, the value our kids get from racing, etc and send it to professional racing organizations, the local fire department(s), driver foundations? Have a raffle. Contact the local news organizations and see if they'll publicize your fundraising efforts.
At the end of the day, if you agree that the equipment is needed, first, do everything in your power to protect your own kids, then, find a way to help everyone get the equipment they need.
I hope you don't take my comments the wrong way. I am not trying to be critical of you or any members of your club. I am just expressing my opinions and hoping that something I share may help in some way.