I own 1 machine gun - AC556. It's registered to me individually - at the time, my Sheriff would sign off on a Form 4. If I were to acquire another NFA item (like have my FNC converted with a registered sear), I'd do a trust.
Here's the thing about Trusts - there are all kinds of trusts. In my opinion, to get a good NFA trust done by someone who really knows what they are doing, $450 is a fair price. But, for $450, I'd want to know that the lawyer who is doing it is an experienced estate planning lawyer who attends the National Firearms Law Seminar put on by the NRA foundation, or a similar seminar that delves into the legal requirements of NFA trusts.
There are folks that will claim that you can get an NFA trust done for about $200. I would be skeptical of those - not saying that they are invalid, just saying that $200 doesn't even pay for 1 hour of attorney time for someone who has invested their time to stay up with estate and NFA laws.