What Do You Need From an API? (Score 1)

I wouldn't exactly call it an API, but DNS Made Easy offers dynamic DNS in a way that seems pretty flexible to me. I haven't used it, but I've been very happy with their service for my static DNS entries - the service is quite flexible, the updates are REALLY fast, and I haven't ever had any problems. It costs me $5 a month, and it sounds like your needs would come to about $7 per month. You do have to pay up front, but I've been happy with them since... hmm, February. It feels like longer (I guess moving twice will do that to you).

DNS Made Easy's dynamic DNS and pricing.

Disclaimer: I'm not affiliated in any with DNS Made Easy, just a satisfied customer. They do have an affiliate program but... I don't want to look like a whore on Slashdot! Sigh, social norms.