use dedicated query:
```
total_cost = DailyExtraCost.objects.filter(
    date__gte=start,
    date__lte=end,
    pricing_venture__in=ventures,
).values('pricing_venture', 'type').aggregate(total_cost=Sum('value'))['total_cost']
```
Using aggregate all sums are done on db side - no need to iterate through list in python