I don't know which program you're talking about, and there are a lot of them out there, so that kinda limits me on answers. The only program remotely like this that I endorse -- and am involved with -- is the Armed Citizens Legal Defense Network, at armedcitizensnetwork.org. I know the people behind it, and the people involved, and have been involved with one successful-outcome case with them already. I'm not in a position to "yea" or "nay" anything else in that vein.
Expert witness testimony? If you're properly trained, your instructors can come in as material witnesses (you're responsible for flying them in and paying their expenses, etc.) and accomplish a large amount of what you'd pay an outside expert for. The material witness can testify to what an outsider cannot: the exact training you received from them, and how well you performed in the course of that training.
Your instructor(s) may well be qualifieable (or already qualified) as expert witnesses on the relevant topics. It would be wise to ask before paying them for training if they will speak for you if you have to do what they taught you to do. It's amazing how many won't...sometimes under any circumstances, sometimes only if you pay them a few thousand dollars a day in fees.
Personally, when I come in as an expert witness, I charge the same as I'd charge to teach a class, per day. Some charge considerably more. The big expense you're going to pay is legal fees and related costs. I take the occasional case at no charge when I feel that the defendant is clearly in the right, is getting hosed, and can't afford to pay what I normally charge. You won't find a whole lot of attorneys who are in a position to do that, though, and as noted, attorney fees and costs are going to be your BIG expense.
The takeaway lesson? Know enough about this stuff to make as close to a perfect decision as is humanly possible, resulting in the sort of outcome that opposing counsel won't want to take to court. Don't be injecting elements into the actual incident that will require otherwise unnecessary expert testimony (i.e., don't be wearing a "kill a commie for mommie" T-shirt at the time you shot your attacker with a handload from your hair-trigger "master of death signature model" pistol, and then panic and run from the scene, pausing only to scream, "I ain't gonna say nothin' 'til my mouthpiece gets here.")
For local prepaid legal fee programs, etc., get what your local providers are offering IN PRINT...take it to an attorney who HAS EXPERIENCE IN SELF-DEFENSE SHOOTING CASES...and expect to pay for their time for their professional legal opinion as to whether it's worth signing up or not.