I found this article that describes how you can meet the ISNIC name server requirements without additional expense.
https://parabing.com/2015/01/dot-is-domains/
It refers you to a hosting company in Iceland that offers a Free DNS service. It took about five minutes to register and add the domain and the IP address for the website. I redelegated the domain in the ISNIC control panel and selected 1984 ehf from the ISP list. I received an email from ISNIC within fifteen minutes confirming the nameserver change.
After I add the MIAB DNS entries, I don’t expect to have to change them at all. Overall, this way is a lot less work to meet the ISNIC requirements and enjoy using Mail in a Box with my .is domain.