[ilaksh]

If it's a small startup I don't think you can beat Replicate as far as costs.

To track usage you need a credits system. Basically you have to read a number from a file, subtract the cost for the operation, and if it's less than zero throw an exception. It does take a little bit of development, but I don't think you need a whole other startup to handle that. You can do the core part of it for one type of operation/cost in less than a day. Maybe a few days to debug something.