As noted above, it would work in a small padded envelope and First Class mail, but it will be $4.00 at least. We sell patches and stickers at one of my companies and occasionally someone will just order 1-2 and we ship this way.
The problem is that the USPS in general is horrible. Our lost package rate is 10x higher with them than other carriers and that is when the majority of our USPS was priority. First Class is/was even worse. I haven't run the numbers in the last 45 days, but judging from customer tickets we are still having a much higher number of issues with USPS versus other carriers even though the other carriers have not been great either.
Since we only ship stickers and decals via that method, we can afford to lose some and just re-mail to get them in the customers hands, but for stuff you can't easily replace/resend, I would be careful with First Class.
DaveW