In The Shawshank Redemption, Andy asks Red to get him a rock-hammer.
But, how did Andy get money to buy this hammer?
If I recall correctly, he didn't carry any cash when he was thrown in prison nor he did any work at the prison to earn some.
Though, this is never explained in the movie, but it is in the novel Rita Hayworth and The Shawshank Redemption. According to the novel, Andy smuggled five hundred dollars with him when he was imprisoned.
The conversation between Andy and Red when Andy required a rock hammer. At the page no. 13-14.
Red: 'How much would an item like that go for?' I asked. I was beginning to enjoy his quiet, low-key style. When you've spent ten years in stir, as I had then, you can get awfully tired of the bellowers and the braggarts and the loud-mouths. Yes, I dink it would be fair to say I liked Andy from the first.
Andy: 'Eight dollars in any rock-and-gem shop,' he said, 'but I realize that in a business like yours you work on a cost-plus basis-'
Red: 'Cost plus ten per cent is my going rate, but I have to go up some on a dangerous item. For something like the gadget you're talking about, it takes a little more goose-grease to get the wheels turning. Let's say ten dollars.'
Andy: 'Ten it is'
Red: I looked at him, smiling a little. 'Have you got ten dollars?'
Andy: 'I do,' he said quietly.
Red: (narrates) A long time after, I discovered that he had better than five hundred. He had brought it in with him.
From the same novel at page number 27-28,
All I know for sure is that Andy Dufresne wasn't much like me or anyone else I ever knew since I came inside. He brought in five hundred dollars jammed up his back porch, but somehow that graymeat son of a b**ch managed to bring in something else as well.
This part is mentioned in the novel 2-3 times. So, in conclusion, Andy smuggled five hundred dollars when he reached Shawshank State Prison.