If you're going to do pressure canning (best for low-acid foods), you may want to start with a regular pressure cooker, rather than a canner.
Yes, it's smaller; yes, you'll have to do more repeats. But you can get a new one for under $100. (And there's nothing wrong with a good used one as long as it has all its parts.) And you might be inclined to use it more
because you're doing small batches. Pick up a batch of asparagus at the farmers' market and do a batch. Clean up and it's over.
New pressure canners tend to run $100 to $300. Again, a used one in good shape is great to find.
But for either kind, the rubber gasket needs to be in good shape, or a replacement available.
Join FreeCycle and ask for unchipped jars. It's amazing how many people want to unload their cabinets and garages. Specify that you want actual canning jars, not old glass mayonnaise jars. Check every used jar by running your finger around the rim, feeling for cracks and chips, which will cause failed seals and contaminated food. Your finger will recognize problems better than your eyes. Check each jar for cracks, esp around the bottom, where a hot jar may have been set on a cold surface (or vice versa) and the bottom is ready to drop out.
Remember that there are regular jars and wide-mouth jars. If I had the option, I would own only wide-mouth jars. They are easier to clean and they hold more types of foods (esp bulkier).
If you do some canning and think you'll stick with it, watch for end-of-season sales for jars, lids and rings. Keep in mind that the rings can be removed and reused after the the jars seal, they're just to hold the lid in the proper position while cooling/sealing. Rings aren't needed for food storage. Just keep them dry, as they rust easily.
Refuse any offers of used lids of the standard type, they are not reusable. The only brand I'm aware of that is reusable are Tattler's, which I have never seen, personally. Tattler's are supposed to be USDA-approved.
Used USDA Canning Guides are fine as long as the edition is 1990 or newer. The guide was updated with safer, more current info. Save some money on a new one by using the online version for a while:
Current USDA Online Canning Guide Sue