I use 10 to 15 tons of hay every year for my operation; we bed pigs with it, feed sheep and cows, and use it for temporary shelters if we need to deal with a pig that farrowed in a bad place. It's useful to have a stack of it, and it's cheapest in June/July when it's made. We pick up up out of the field for the best price, but that means we have to be ready to get it under cover as quick as we can.
A note on hay costs: the least expensive way to buy hay around here is huge bales. Either 800lb round bales, or huge square bales - 4x4x5, for instance. Purchased in huge bale form, you pay $120-150 a ton. If you buy the same sort of hay in small square bales, it's $250-300 a ton. I have a tractor capable of handling the big bales, but I prefer to use the smaller ones for bedding purposes. For feeding cattle, the big bales are the way to go. Picking the hay out of the field gets me a price of $150/ton, inclusive hired help, stacked in my barn. Hoping that this gadget will allow me to reduce my cost-per-bale for field purchases.