I buy my prepaid envelopes on line. They come with either a preprinted tracking number or a set of stickers. They are " forever" like the forever stamps, so i just use them whenever. They are $5.--. Can't remember exactly. So, it's still over $20. They are fairly flimsy cardboard so i beef it up with some tape. No weight limit that I'm aware of . Has worked so far. Hate to not see you on these!