They should be paid but very minimally paid. Because of my spouses job I am very familiar with the way the prison system works. People would be appalled if they knew all of the perks prisoners have. They get free education, medical and dental, they get to have TV's, game systems, radios, musical instruments and much much more in their cells. They are paid a small stipend simply for being inmates whether they work or not to enable them to buy their basic foods and toiletries. Everything they need is provided for them, if they want more then they should work for it, but the pay should be minimal, they are there for punishment not for the country club some of these prisons are turning into.
I think prisoners are in some ways a financial burden, since housing, feeding and medial care during incarceration cost money. I do think some prisoners should be able to earn money for work, but they should also have to contribute to the cost of their upkeep. They should have some work duties that they can earn for, and others that go towards their upkeep.
Crime is costly to our society and imprisoning criminals is very expensive. Taxpayers should not be under an obligation to pay prisoners for work performed while they are incarcerated. Any money that a prisoner earns should be used to pay back victims and/or pay back the taxpayers for the cost of keeping them in jail.
Prisoners are being given food and board and they have all of their medical needs taken care of. The work they do is supposed to keep them busy and to help pay back the prision for the cost of housing and feeding them. Prisons loose lots of money each year.