##views.py
def pg_session_addedcost(request, pk = 1):
    user = request.user

    if not user.is_authenticated:
        return redirect('autherror')

    curSession = Session.objects.get(id = pk)

    if request.method == "POST":
        print (request.POST)
        newAddedCostForm = AddedCostForm(request.POST, request.FILES)
        if newAddedCostForm.is_valid():
            newAddedCost = AddedCost(
                comment=newAddedCostForm.cleaned_data['comment'],
                session=curSession,
                image=newAddedCostForm.cleaned_data['image'],
                cost=newAddedCostForm.cleaned_data['cost'],
            )
            newAddedCost.save()
        else:
            print (AddedCostForm.errors)


##forms.py
class AddedCostForm(ModelForm):
    class Meta:
        model = AddedCost
        fields = ['image', 'comment', 'cost']


##models.py
class AddedCost(models.Model):
    session = models.ForeignKey(
        Session,
        verbose_name= 'Смена',
        on_delete = models.CASCADE,
        default=0,
        blank=True,
        )
    image = models.ImageField(
        'Сопроводительное изображение',
        upload_to = 'images/forSession',
        )
    comment = models.TextField(
        'Комментарий',
        blank=True,
    )
    cost = models.FloatField(
        'Дополнительные расходы',
        default = 0,
    )


##HTML
{% load widget_tweaks %}

<form method="POST">
                                {% csrf_token %}

                                {% render_field form.image %}<br>
                                {% render_field form.cost %}<br>
                                {% render_field form.comment %}<br>

                                <button type="submit">
                                    Добавить
                                </button>
                            </form>