Cost of living is actually pretty cheap for the Cuban. On average, their wages can go from $10 (CUC) month to $25, and some jobs much higher.
They get food allowances, and don't pay for housing or utilities the way we would. Women get "product" allowances, that usually run out before they are done. Depending on where they work, (those on resorts) they will get tickets for the "worker" bus, meals, and sometimes even clothing from their employer.
Most of the expense that a working Cuban will face are those like clothing, shoes, and other non-essential items. Once you take away food, shelter, utilities, transportation...there's not a lot of "cost of living" left over. A Cuban not working, or in jail, is a financial burden to the family...which is why they don't like to end up in jail.
This is why, for the most part, people are grateful for gifts brought by tourists. Those in the tourist industry get much more than those that are not.