tamalita, I think that with the original intent of billing was to simply be able to bill a person out at a certain rate. Since it was developed, the need for more flexibility has presented itself in other threads, like
this and
this. You had replied in another similar thread
here, where I assume you hadn't actually tried playing with billing just yet.
I think you likely understand the limitations: billing is simply per user, and not a very flexible system at this time. So given this limitation, you have only a few options:
1. Do not use OG for billing, just wait until and if better billing features are added.
2. Try a workaround, such as creating multiple fake clients, each with a different billing rate (example, client "Jose Smith-25" at $25/hr billing rate, and client "Jose Smith-35" at $35/hr billing rate etc). See if you can get creative to solve your problem.
3.
Sponsor the feature.
I myself have offered this as a feature suggestion, as I would love to use it for my own more complex billing needs. Only time will tell if it is on the roadmap.
cheers