One option we have seen work well at the shop I work at is the Silencerco "Easy Trust." $139 is affordable, and I figure since Silencerco is a large driving force behind the Hearing Protection Act, they have some spiffy suit lawyers that helped make sure it is valid. But...Silencerco is going hipster, so who knows what their lawyers wear.
When I had my trust created, I went through guntrustlawyers.com, and paid a lot more. Silencerco's option didn't exist at the time.