To avoid having to buy those adhesive shipping labels from the store try recycling old index cards or any other type of paper to put addresses on boxes you are mailing. You can use blank index cards or blank paper, write the return address on one piece or at the top of the card/paper and then the shipping address on the other piece or lower part of the card/paper. If I do that, I usually write "To:" and "From:" in front of the address to make it clear which is which.
Then use wide clear packing tape to attach the "label" to the box with the shipping address towards the middle of the top of the box or the one piece paper/card in the middle of the top of the box. I use two pieces of tape as one piece usually isn't enough to completely cover the label. It works best to completely cover the address label with tape so it doesn't come off in the shipping process. Just don't cover the entire top of the box in tape as the post office can't put its postage stickers or any other markings over the tape, just a small piece or two that just covers the label with about a 1/4 inch overlap will work.
I have not had to buy self-stick labels since I've been doing this and have never had any problems with the labels coming off in shipping. It also helps, just in case, to put a paper or card inside the package on top of whatever is in the box so that if the label should come off the post office can look for an address in the box.
You could print your index cards on the P. C. to save time. Use the 4x6 photo slot or print as envelopes. may God bless you.