[languagehacker]

The other folks commenting that it depends on your costs are spot-on. The following are important data points for getting your economics right:

0) Advertised SLA. What uptime and response time are you guaranteeing your customers?

1) Minimum cost of the platform (i.e., no traffic). From here, also determine what full utilization looks like in terms of max number of API calls within your advertised SLA.

2) Cost of platform at scaled utilization based on load projections. This is where you can figure out how to make money when negotiating committed or volume-based pricing for specific customers.

3) The overall human cost of building and maintaining the platform. Don't forget that you're not just covering the price of running the platform, but the time that you and possibly others have put into it. The last thing you want is for success to force you to make your platform more expensive because it's grown past the available sacrifices a single person bootstrapping an application can make. You'll be able to retain and delight customers better if your pricing model accommodates a mature business that supports actually paying someone a salary from the get-go.