Reddit mentions of Pratt PRA0023 100% Recycled Corrugated Cardboard Box, 9" Length x 6" Width x 4" Height, Kraft

I won't speak to the value of in-box vs out, because I don't know enough to give good estimates.

eBay does take 10% of the final sale price (including shipping), which is why Pops are more expensive there than on marketplaces like Funkoswap/Facebook. eBay will give you a bigger audience, but it does have the cost aspect you need to account for. Keep in mind that all of your sales (if using Paypal) will be subject to Paypal's 2.9% fee (I believe that's the right amount, not 100% sure). I sell most of my stuff on eBay. The net is about the same as if I sold it on here or Facebook, but I like that eBay is post-and-forget and I don't have to negotiate over PMs and replies for a long time before finally selling.

Packing materials are easy to come by. I sell everything in box, so I buy 9x6x4 boxes on Amazon in packs of 25. You can pick up similarly sized boxes at Walmart or presumably any department store with an office supplies section. Likewise for big rolls of bubble wrap, packing tape, and packing paper. Boxes should be around $0.50 a piece in-store and bubble wrap I'm not sure about.

I print all my shipping labels via USPS, either Priority Mail (2 day shipping, costs about $6.75 per Pop) or First Class (2-3 days usually - about $4.50 per Pop). You can print labels right off of the USPS site and tape them to the box, and then you just drop them off at your post office. If you sell on eBay, you get a discount on the label cost. A label that costs $4.29 on USPS costs me $3.88 when purchased through eBay's seller portal. I've never had a Pop arrive damaged with the way I package and via USPS. Even though I've never had something be damaged, anything I sell over $75 or so, I always insure at my own expense (usually about $3-4 for insurance).

This is essentially exactly how I ship, but I use packing paper instead of a plastic bag to secure the Pop from bouncing around in the box: https://www.reddit.com/r/funkopop/comments/3q29x4/showing_how_i_ship/


These are the boxes I primarily use: https://smile.amazon.com/gp/product/B00E81LBCS/

And this is the packing paper I use: https://smile.amazon.com/gp/product/B004HMIQ8A/

this is what i use, love em.

Don't know about the rest, but baseball caps I would suggest picking up boxes like these 9x6x4:
https://www.amazon.com/gp/product/B00E81LBCS/ref=oh_aui_detailpage_o07_s01?ie=UTF8&psc=1

They can still be sent First Class and it protects the hat from damage.

Here's 25 of the 9x6x4: https://www.amazon.com/Pratt-Recycled-Corrugated-Cardboard-Standard/dp/B00E81LBCS/ref=sr_1_16?ie=UTF8&qid=1506435576&sr=8-16&keywords=shipping+boxes

http://www.amazon.com/gp/product/B00E81LBCS?psc=1&redirect=true&ref_=oh_aui_search_detailpage

I use these.

https://www.amazon.com/gp/product/B00E81LBCS/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

these are the boxes I use, actually bigger than what you recommended. They are thick and sturdy. I wrap the pop in bubble wrap(like a gift), tape it up. I then use packing paper around the pop to act as bumpers so it doesnt get dinged from something hitting the box.

This is a good size box and free shipping if you have Amazon Prime

https://www.amazon.com/gp/product/B00E81LBCS/ref=od_aui_detailpages00?ie=UTF8&psc=1