Send a bill or proposal to clients

I want the ability to send a custom bill or proposal to a client and let them accept and enter their own payment info. 
I do not want to create a separate order form for every possible combination of services and discounts applied. There are too many combinations. There are many occasions where custom packages are built. Why is this not a thing already? Many other CRMs have this ability.... to create and send a custom BILL/INVOICE that the customer can pay. I know I could take the payment info on the phone, but that is not how I want to do it. The system seems limited.