Domain availability API? Or other options?

I'm writing a script that automates a large portion of my domain research. I need to find a suitable API (or other option) to loop through a list of domains and determine if they are available or not. I know reseller accounts on eNom and Dynadot have APIs capable of doing this, but then I have to be setup as a reseller, which can be pretty pricey. It's not like I have any need for a reseller account other than API access. Are there other options? I need to burn through around 100k potential domains a day. Can the reseller APIs even sustain this? Any suggestions for what to do here?