Hi,
I do not think there is any, since it is rather a complex logic, otherwise ABAP forum is the best place to look after any similar experience.
Basically you got two standard options for monthly budget control:
1. Through budget release function, so that is kind of manual option to release periodic funds and have availability control based on released budget. That will be cumulative logic, means unspend budget will roll forward so to speak.
2. Having a substitution user exit to get additional statistical account assignment object for budget control, in this case it can be only internal order.
Regards,
Paulo