Annotate example

example.py

class Company(models.Model):
  name = models.CharField(max_length=100)

class Product(models.Model):
  name = models.CharField(max_length=100)

class Quotation(models.Model):
  product = models.ForeignKey('app.Product', related_name=quotations)
  company = models.ForeignKey('app.Company')
  price = models.DecimalField(...)

queryset = Product.objects.annotate(min_value=Min('quotations__price')).values('name', 'quotations__company', 'min_value')

for product in queryset:
  print product['name'], product['quotations__company'], product['min_value']