I am creating a website to learn the django framework. It's a website for a web development studio where you can customize the project that you need them to design.

My model architecture is:

Features: the smallest building block.
Bundle: a group of features that you want to include in your website.
project: the overall collection of features, that can include (or not) one bundle.

```
from django.db import models

class Feature(models.Model):
    name = models.CharField(max_length=100),
    price = models.DecimalField(max_digits=6, decimal_places=2),
    description = models.TextField(),
    progress = models.IntegerField(),
    duration = models.IntegerField()

    def __str__(self):
        return self.name

class Bundle(models.Model):
    name = models.CharField(),
    features = models.ManyToManyField(Feature),

    def __str__(self):
        return self.name

```

This is what I have so far, it's not complete but you can get a taste of what I want to do. The problem is:

I want to include a field in bundle and project that calculates the total cost of it. The field's value will be the sum of the features included in the features attribute of my bundle class.

How can I accomplish this? Can I create a field that is a list of objects' features?

Thank you in advance.