Looking for Feasibility of Phone Call to Text API

I have an idea for an app, but am trying to understand the feasibility of it. The basic needs are for an API to call a user, the API says a few prompts (3-5) and the user responds for about 10-15 minutes. The software records, transcribes and saves the voice data. For these functionalities we need the cost to be as low as possible, and ideally under $10-15/month per user to achieve profit and feasibility. What APIs would you recommend that provide low cost and are good to use.