I, too, raise my own mice and rats. The point I was trying to get at is even if a mouse/rat is underfed and/or dehydrated, that does not mean that the prey item has little to no nutritional value. The prey item may have less nutritional value when compared to a well-fed prey item, but it still has nutritional value.
I feed my colonies a lab block diet. They always have food and water, and I really see no need to 'gut load' them. The lab blocks are a complete dietary source (I do occasionally give them treats), which does not need supplements. However, if a person does 'gut load' their mice/rats I would definitely consider the cost. $5 dollars seems reasonable, and not to much of an increased cost, so I see nothing wrong with it for that reason. Yet, I would still question the need in conjunction with any ill-effects that may occur. Snakes in the wild have eaten wild, non-gut loaded prey for longer than we all know. I do realize that we try to provide the best care for our snakes, so added nutrients would seem like a plus. Although, what is really in the supplements? I also ask, can a surplus of some minerals (i.e.calcium) that are in the supplements lead to problems in our snakes.
Snakes digestive acids are extremely strong. They are able to break down virtually all of the prey, and as a result, the snake uses/absorbs a large proportion of the nutrients (probably more than most animals, for the fact that the amount of time it takes for a snake to digest and then pass the waste). In my opinion, I would be cautious in using supplements.
Finally, part of the reason for my previous question and now my subsequent rant is because I have been irritated lately with the countless number of baseless, altogether wrong, and assuming/guessing posts. If you are not sure or have no experience on the specific matter then either don't post or put maybe/possibly/probably or I'm guessing but not sure in your response to questions. People come here to seek advice and correct answers. The last thing we need on this board is wrong information, then we are no better than many petstores stating things as fact, when they are completely wrong.