Recently, on my weekly visit to the Salvation Army Thrift Store, they were having a $5.00 Bag of Books sale on. I was able to pick up some useful books about gardening in my area, plus some other interesting tomes I had previously considered buying such as a book of poetry by Robert Service. I particularly love "The Cremation of Sam McGee" which my grandfather used to recite from memory.
I think that most of us who are prepping take full advantage of our thrift stores as someone else's trash just might turn out to be a treasure that helps us become more self-reliant. Just the other day, I found a hand cranked meat grinder with all the attachments on a mounting board for a fraction of the cost of new. I have also seen a hand-operated knitting machine, treadle sewing machines, and other manual treasures discarded in favour of electric devices; also paper plates and plastic cutlery, canning jars and sealing lids still in the boxes unopened, hand tools of good quality, real wool woolens, kerosene lamps, oil lamps, camp stoves, a wide variety of camping gear, backpacks, and all at reasonable prices compared to buying new.
Another great source for prepper items is yard sales, and even dumpsters. Right now, I have professional pizza pans that were rescued from the dumpster behind a pizza shop in town. Some elbow grease and they were as good as new.
In my town, every spring we have a weekend "swap" event, where folks put out things they no longer have a use for at the curb, and other folks cruise around and pick up stuff they think they could use. After the two day event, the "unswapped" items are collected by the city and donated to a local charity. Check in the papers, or the city's web site to find out if there are events like this where you live.
Remember, prepping doesn't mean going out and spending big bucks on special gear. It means developing the survival mindset that enables you to see the value in someone else's junk and re-using, recyling, re-inventing. It means seeing opportunities where other people see none. It means reaching out and grabbing opportunities to do for yourself instead of waiting for someone else to do it for you. And sometimes it means climbing over obstacles nay-sayers might put in your path.
A great many sites out there are very focused on selling you things to prep with, but really, do you really need to spend a great deal of money in order to be prepared? No, I don't believe so. Rather, if you are frugal, and use your money wisely, you can be prepared for many of the "negative events" that life and the universe can throw at you without spending a great deal more than you did before you realized that you need to become more self-reliant. Rather, you will be spending your money differently.
For this reason, I do recommend that you look not just at prepper sites, but also at sites about how to make your dollar stretch further, on how to simplify your life, and live frugally. Read the blogs by people who can foods for fun, and tell you how to do it. Check out the blogs of folks who camp, and hunt, and fish for fun. These folks don't think of themselves as preppers, but really, many of these folks have a survival mindset.
For example, one fellow who hikes and blogs about his various treks posted about how he started using socks to house a lot of his smaller pack items which allowed him to move more quietly when he wished to be able to photograph wildlife. He also found that socks provided cushioning for delicate gear such as the lens of his cameras; and at need, he also had additional extra socks for his feet, to use as oven mitts, and to carry found items.