Best Way To Ship A Coin First Class?

It all depends on weight. Do you really mean First Class mail, or do you mean regular mail?

Go to the USPS website to learn the different shipping categories and their associated costs for varying weights/volumes.

Having worked on the letter sorting machines for the Postal Service
back in the day , the tech would go nuts when they had to fix a belt due to a coin
In an envelope jamming the machine . After five years or so he had quite a collection .
DONT SHIP coins in a piece of Letter Mail , they don't mix.

Thank you. I appreciate it.

This has been covered in lots of other threads here.

What many of us do in this situation is put the coin in a clear plastic flip, attach it inside a piece of folded thin "cardboard" (think about the thickness of a greeting card) that is close to the size of the envelope.

If less than an ounce, it costs you a 55 cent stamp. I do this for single coins up to quarter size, and I charge 63 cents (55 cents times 1.13 to cover the ebay and paypal fees).

You must consider that when you do this, there is no tracking, and the recipient can say they never received it (and maybe they didn't for reasons mentioned by others). WHen this happens, you must refund them. My experience is that this might happen to 2-3% of your shipments without tracking.
It is also true thatr the postal system is all screwed u right now, any all shipments without tracking are more risky (I just reported in another thread on a shipment that eventually reached the buyer after 8 weeks ... I already gave him a refund around week 3).

Good luck!

Edit: As TNG says, you can use a 70 cent stamp and write or stamp "Non-machbinable." I do this for half dollar size coins, and use thicker cardbord (I use cereal boxes), or multiple coins (often kicking it up into a higher weight category ... but it's still much cheaper than the padded envelope route. At 2 oz and non-machinable, you are looking at only 95 cents."

I have ships hundreds and hundreds of cents via regular mail (uninsured) by securing them between two thin sheets of cardboard, taped carefully, then applying postage according to weight - never had a single one fail to arrive.

That is a fair statement.

following this conversation with interest. I have sold a few coins recently.. For a Silver Dollar/Eagle sized coin, it is clear that USPS shipping with tracking and in a bubble or good quality envelope is the way to do it.
For smaller coins, it is likely that a standard envelope and stamp would be fine, but what about selling a 40% Kennedy, for the value of one of these, this would have to go as the cheap option, but is it too big for this?