Are you allowed to have outside money sent to you in prison? And do prisoners deal with cash in prison or Debit type cards?
you have money sent in and put on your "books", sorta like a bank account. actually, there's two accounts... a "spend" account and a "frozen" account. there's a monthly limit though, which varies state to state. for instance if your $135 in 28/30 days.. so if you have $235 sent in over that period, 135 (which is also the Max you can have in your spend).. the other 100 will get put into your frozen, but the prison will take a percentage of it first, so you'll get something like $50 in your frozen (for when you're released... now, you can sometimes use the Frozen account to buy things like TV's and typewriters and guitars, ect... but you need approval from the Unit Manager.. the guy/girl who manages your "block/unit").
now, you use that money to buy shit on commissary... food, pens and paper, shampoo, razors, ect... you can also get coins like a max of $18/wk in quarter and dime tokens to use in soda machines and buy ice cream treats at lunch......... OR you can use those quarters to gamble with and pay debt.
in county jail, I dunno if there's a limit on how much money you can have on your books... like if you come inand get arrested with $3k in your pockets, that same $3k is yours when you're released... now if you go to prison, you'll keep 135, and 1500 (or so, minus the 135) will go into your frozen, and the prison will keep the other 1500.
for example... you go to prison... you have your books full at 135... you can spend a max of $30/wk... you get 18$ in coins, the rest you buy peanut butter (for yourself.. 3500kcals in a jar), then you buy 50-100 ramens, 5 boxes of little Debbie snacks, ect..
now you're in business.... you "store out".. i.e. LOAN your ramens out each week... 2 ramens for 3 back, 3 for 5, 5 for 8, 10 for 15, ect..... and your little Debbie snacks you store out 1 box, to be replaced with a box the next week PLUS $.50 coins (per week).... or you loan out the coins...
essentialy you're a loan shark... charging 50% interest weekly..... that's how you survive in prison.. now, if a guy can't pay... (a $5 loan that turns into $50) is the best thing... because you can sell the debt for $30 to a guy who'll beat the guy up (if you start beating guys up, you're going to the hole and losing your income). now $5 turns into $30... and you do that week after week with multiple guys... and so long as youre fare and respectfull and don't let anybody rip you off, nobody is gonna tell on you.