Django Admin is the CRUD interface of Django web framework. It is mostly automatically generated but can be widely customize. However, you must keep in mind that it is designed for trusted users only and has its limits. In any case, you must never give admin access to untrusted users.
Django Admin provides a high level of customization, but be careful of not falling too much customization details. If you do so, it's probably time to create you own custom interface without Django Admin at all.
I don't think you need get_price(self) specially when you are not making any changes to the price variable. I would remove the method get_price since you can get the same value from the price under the product model. I could be wrong. Just don't see the value of get_price method here.