Funny seeing this. I've been working on a site to allow people to send a letter as cheaply and conveniently as possible. I actually think letters (physical) are a great way to make an impression, often times much more so than an email. Had never considered sending an actual object lol.
At current scale (which is very small), the cheapest I can get it down to without losing money is $1.55 per letter (postage, paper, print, envelope, stripe fees, misc. hosting fees, etc.). Sadly, I have no way to compete with a $0.25 lime!
If you're curious, https://mappymail.com
What if you also start providing the 0.25$ lime feature as well (by making use of the amazon prime itself as well?) xD?