How would you characterise the fallacies in this statement: "If prisoners receive free meals, why don't students- our future doctors, artists, engineers, etc.- also get free meals?

We can reasonably say that there is an implied analogy here: prisoners are like other groups. It is a (very) weak analogy because prisoners are under the care of the another group (state, federal govt, etc) while they are prisoners and don't have the ability to earn money for food (unless given the opportunity). I am not an expert on the prison system, but I believe prisoners do work and get compensated very little financially, which might mean they are not getting "free meals," in which case this would also be an example of begging the question .

Prisoners don't receive free meals, they are made to work.
They are also made to work on themselves. These prisoners are also working for us, by not being in the society they are in fact, not doing harm, i.e. no crime, consider it a tax that you pay for preventing the greater loss. They don't get to choose the food they eat, the quality of the food or the type of food and at what time they get to eat. All of these are determined by the authorities.

So do you wish to feed these students, doctors, engineers, and doctors, the food they don't wish to eat, at the time they don't want to eat and at quality standards prescribed by the authorities?

This 1984 all over again, longing for Big Brother aren't we?

If prisoners don't pay for toilet paper, why do students, doctors, me, you, etc. have to? Prisoners get free room and board....etc. Prisoners are a group like any other, false analogy fallacy.