Buy Bag Of Cement

I am planning on laying down a patio on a small budget.About 15x20 im not working so time is not a factor.I would think getting bags of cement and mixing it your self would be cheaper but when i looked it up online how many pounds of cement made one yard the only thing i could find was wikianswers and it said 3240 which comes out to 53 bags of 60lb cement at 3.00 is 159.I have.