You could ship it in a business envelope for less than a dollar. That's the cheapest and most subject to loss or damage.

You could put it in a coin holder and send it 1st class mail using PayPal with $50 insurance included for about $2.

You could put it in a box and send it Registered mail, insured for $100, for about $20.

For a hundred dollar chip, I'd choose the second option, which is essentially what Steve suggested.

Insurance from the USPS is expensive, especially if you ship a lot of chips. If you only ship one a year, I'd suggest paying the $10-12 for Registered mail without insurance; Registered mail is almost NEVER lost and you are taking almost no risk of loss.

https://about.usps.com/who-we-are/postal-history/hope-diamond.pdf