I'm going to assume that each bill is a Django model object. The easiest way to do this calculation in Django is to add it as a function to your model:

# models.py
from django.db import models
import re

class Bill(models.Model):
    full_name = models.CharField(max_length=30)
    food_name = models.CharField(max_length=30)
    qty = models.IntegerField()

    # Ideally, you would represent the price using
    # a DecimalField. 
    # price = models.DecimalField(decimal_places=2)
    # only = models.BooleanField(default=False)

    # However, you said you're using a string instead.
    price = models.CharField(max_length=20)

    # If price was a DecimalField, you could do a simple
    # calculation.
    #def total(self):
    #    return self.qty * self.price

    # However, since it's a string, you'll have to
    # convert it to a whole number first.
    def total(self):
        """Computes the total bill from the quantity and price."""
        # Remove non-numeric strings like 'only'
        # from the price. Warning: this will remove
        # decimal points too, so it only works with
        # whole numbers as prices.
        price = re.sub("[^0-9]", "", self.price)

        # Convert it to a whole number so we can do
        # math on it.
        price = int(price)

        # Return the calculated result
        return self.qty * price

You can call this function in your template by typing its name, without parentheses:

<td id="total">{{ bill.total }}</td>

Please be careful about how you represent currencies. If you need to represent fractional amounts, use a DecimalField with an appropriate number of decimal places set; otherwise, use an IntegerField. You should never use a FloatField to represent currencies, as it does not always store an exact representation of a currency amount.