Need a person well versed in Kohana Framork

First of all, you need to connect Robokassa with a slight change in the site itself:
Accordingly, you need to connect to the site Robokassa.
There is an option when you can make several buttons separate by type of payment (so do).
Options for payment from RoboCass: Payment by card, Payment by Yandex.Money, Payment through Qiwi terminals, Payment by Webmoney, Other payment methods (RoboCass).

In the admin in the setting of cities add the choice of payment method (from robobox) and add your (type of cash payment). Now there is the same interface, but for delivery cities (i.e., the same interface). just copy it.

Orders that have been paid (or just clicked the button - payment through Robocast (well, its variants)), then in the adminka should be the status of the order: Invoice (moved to Robocasta and pays - there is time for payment), Paid (invoice paid), Not paid (not paid)

Also, users should display their orders with statuses from the admin, and payment buttons from Robokassa (if you did not pay, or failed) and payment status, if it turned out.