How to receive SMS OTP from 50 SIMs in real-time?

Hi, I have around 50 SIM cards and need to receive SMS OTPs through an online system (API or web).

I know SIM boxes can do this, but they are expensive and hard to find.

Are there cheaper and practical alternatives, like using multiple Android phones or USB GSM modems?

I need near real-time SMS and the ability to send it to my backend.

Any advice or experience would be appreciated. Thanks!