is there any middleware that charges by volume and not endpoints? i know celigo is the go-to but $500/month feels excessive for the amount of requests we'll need (sending ~120 sales orders monthly to a partner company's system)

Zapier?

Hey - I am with Celigo. Do you mind sending me a note to rico@celigo.com or DM me so I can understand your use case a bit more and see if we might have some options for you?

I recommend Boomi ($99 per month + usage-based pricing (no upfront cost)) or Pcs (non-endpoint based, "pay-as-through" pricing). Good luck.

i am a technical consultant. i can do this without any third part, just using Restlet. DM me to discuss