ightwave

I prefer unit pricing eg. 0.08/invoice and say 0.02/invoice for online payments feature

don't charge per month or for whitelabel (charging for reselling is ok) free tier

https://www.ssllabs.com/ssltest/analyze.html?d=entrydns.net

0 out of the top 1000 Alexa domains are using dnspod.com so...

dnsmadeeasy.com - $30/year - anycast - Google for their uptime record.

or if your site isn't worth the $30 just use your registrar's free dns.