First off you should realize that the registrar’s and domain name servers don’t have to be the same. Feel free to use any registrar (ex: namecheap, gandi, etc) and host the domain name server anywhere else.

Secondly, if you want a good API for dynamic updates, I’d recommend looking for something that supports nsupdate, which is bind’s built-in update mechanism. It’s supported almost everywhere, including by let’s encrypt clients like Lego.

Some (probably most) domain registrars allow to use different nameservers. So for example i use namecheap, since its cheap as domain registrar but cloudflare for DNS, since the API is free and widly supported.

I’ve been happy with whc.ca for hosting…been using their pro account for years. I generally use canspace.ca for domain registration, and have done so for more than 10 years without issue.

I’d suggest using OVH. https://help.ovhcloud.com/csm/en-ie-dns-dynhost?id=kb_article_view&sysparm_article=KB0051641

Depending on your country you may need to use ovh canada

Cloudflare is by far the cheapest registrar & host I’ve used. I’m on their free plan, which can handle almost any load (thousands of requests a week for me personally). The domains are sold at cost, so around $10 for my dot-coms. So $10/yr covers it.