We developed a custom program for our client to address this issue. We created a z-table to update budgets for capital requests. We entered these capital request numbers in internal orders (order types with investment measures) & also continued maintaining budgets at the individual internal order level too via tcode KO22. We activated a user-exit which enabled automatic reference between the internal order/s & the capital request. Multiple (or single) internal orders could refer to one capital request & the total budgets maintained in these internal orders couldn't exceed the ultimate budget maintained in the z-table for the capital request.
You may be able to achieve something similar for your requirement. Create a z-table for the combination of entries such as capital expenditure number, plant, profit center, etc and enter the final budget here. Reference this capital exp # in internal order master data & activate the user-exit. Try this in your sandbox to see if this solution would work for you.
Regards,
MG