title: Making many-to-many relationships with different price for different customer
body: <p>I have three models <code>Product</code>, <code>Buyer</code> and <code>Offer</code>.
  Any buyer can inquire about any kind of <code>Product</code> but for each customer I might offer a different price.</p>
  
  <p>The net price of a product is already given by the supplier.</p>
  
  <p>I wrote the code below and suddenly realized I can only select products for an offersheet but cannot give a different price every time for each product and for each customer with this code.</p>
  
  <p>It would be nice if anyone could give me some suggestions.
  Thanks.</p>
  
  <pre><code>class Product(models.Model):
      name = models.CharField(...)
      net_price = models.NumericField(...)
  
  class Buyer(models.Model):
      name = models.CharField(...)
  
  class Offer(models.Model):
      date = models.DateTimeField(auto_created=True, auto_now_add=True)
      buyer = models.ForeignKey(Buyer, default='',)
      products = models.ManyToManyField(Product, related_name='offer',)
  </code></pre>