how many are you looking to buy? I got a pack of 50 from Amazon for $6. These were the ones I got and I guess the only thing I would note about it is that it's definitely a small mailer. With a pack of clamshell wax tarts, there's probably enough room for one more 10 mL rollerball comfortably. I can shove more in, but these are definitely small. I like them for sunday destashes though since most people don't buy too much so 95% of all the orders fit in there. With larger orders, I recycle the padded mailers I get. You can probably get more for cheaper if you look around, but I like Amazon so.

Edit: Oh and get packaging tape. That's the only acceptable tape. I found that out first time I tried to mail something haha. With those mailers, I don't use packaging tape though because they have a seal, but it's nice to have around. Last tip: addressing. You might already know this, but I didn't before and I messed it up two separate occasions before I remembered. Your address (the "from" address) always comes first and is on top. The address you're shipping to is on the bottom. I kept mixing them up when I first started mailing things because my logic was that you'd want the "To" address on top because that's the more important part right? Nope. "from" address is on top. These days, I put my address in top left, address I'm shipping to in the middle, but sometimes I make a label from notebook paper and for those, I just stack the addresses vertically on top of each other with my address on top.