As far as I can see, you have a developer licence plus subscription and priority support, which means that you can download the RadControls' source code from telerik.com after logging in and going to "Your Account", and then to "Purchases and Downloads" :
By the way, you don't need a RadInputManager for each RadGrid item. You have to add the textboxes from every item programmatically to the InputManager's InputSettings. Here is an example:
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