First of all, you need to know something about the growing season in your area, and when various kinds of produce will be available. For example, trying to freeze strawberries in August would be a poor idea -- at least in my area there aren’t any available then. Proprietors of fruit and vegetable stands may be able to tell you when what is available. Or you may be able to get such information from the local office of the Department of Agriculture.
Where do you buy produce in large quantities? Certainly not in the supermarket! If you live in the country it shouldn’t be too hard to find a large produce stand or perhaps a farm where they allow people to pick the produce for a lesser price. This latter suggestion may also be open to city dwellers who have transportation. In the city there are big markets where farmers bring in their produce to sell, mostly to retailers. The prices at these markets vary according to demand. I would suggest you shop a couple of days before buying to get a feel for what is a good price. If you can buy when they have an oversupply of produce you’ll get a good deal. Also, watch for the produce that is reduced because of being very ripe. Last year I purchased a box of 12 pineapples for 50 cents that were almost overripe. That gave me some to eat, some to share, and some to make into preserves. I have also picked up produce that has been thrown out because of being spoiled and found that some of it was still good. And that was free.