If you are only teaching LTS- there is a LTS professional membership that costs $12 and comes with insurance. When I don't have tests to put out, I don't join a club, it's just too expensive, and my rink has always covered this fee- I get a card and it says "instructor" on it, but it's the same basic skills card the kids get.
You might have to register THROUGH LTS to do this though, as it's a basic skills membership.
I've never heard of the $40 only, but I worry that's a "fan" or "parent" thing- since it's so much different from the individual member fee- seems "too good to be true" price wise. You probably carry your own insurance, so maybe you don't need USFSA's coverage in anyway, but I'd bet this option does not include the sport insurance and such.