Automatic subdomain/domain creation script at digitalocean

I want to integrade with my php a server script that creates automatic subdomains and/or domains at digitaloceans servers. The dns resolution will be handled by a bind9 dns server so, it's a requirement actions like create/delete/modify dns records. I would like to hear about the economic cost of what you propose in relation of server fees, data fees, service cost etc. once a box is up and running.