You should look into pyformat when you only want to play around with the string representation.

>>> cash = 13.14
>>> '${}'.format(cash)
'$13.14'
>>> cash = 3.4
>>> '${:.2f}'.format(cash)
'$3.40'
>>> values = [1.2, 65.32, 15.2345]
>>> template = 'Stuff costs ${:.2f}.'
>>> for value in values:
        print(template.format(value))


Stuff costs $1.20.
Stuff costs $65.32.
Stuff costs $15.23.

You could also play around with object oriantation and manipulate the specific string manipulation:

>>> class Dollar:
        def __init__(self, value):
	        self.value = value
        def __add__(self, other):
	        return Dollar(self.value + other.value)
        def __sub__(self, other):
	        return Dollar(self.value - other.value)
        def __repr__(self):
	        return 'Dollar({})'.format(self.value)
        def __str__(self):
	        return '${:.2f}'.format(self.value)


>>> d1 = Dollar(1.2)
>>> d2 = Dollar(4.63)
>>> d1
Dollar(1.2)
>>> str(d1)
'$1.20'
>>> d2
Dollar(4.63)
>>> str(d2)
'$4.63'
>>> d1+d2
Dollar(5.83)
>>> d1-d2
Dollar(-3.4299999999999997)
>>> print(d1+d2)
$5.83
>>> print(d1-d2)
$-3.43
>>> price = Dollar(0.99)
>>> 'The price is {}'.format(price)
'The price is $0.99'

See, with this double underscore methods you can mess around with the power of python. __add__ let's you override the plus operator, __str__ controls the string conversion and __repr__ the internal interpreter representation.

Of course you should convert your values to Decimal compute with that to avoid aweful rounding errors:

>>> from decimal import Decimal
>>> str(Decimal('0.1'))
'0.1'
>>> class Dollar:
        def __init__(self, value):
	        self.value = Decimal(str(value))
        def __add__(self, other):
	        return Dollar(self.value + other.value)
        def __sub__(self, other):
	        return Dollar(self.value - other.value)
        def __repr__(self):
	        return 'Dollar({})'.format(self.value)
        def __str__(self):
	        return '${:.2f}'.format(self.value)


>>> d1 = Dollar(1.2)
>>> d2 = Dollar(4.63)
>>> d1
Dollar(1.2)
>>> str(d1)
'$1.20'
>>> d2
Dollar(4.63)
>>> str(d2)
'$4.63'
>>> d1+d2
Dollar(5.83)
>>> d1-d2
Dollar(-3.43)
>>> print(d1+d2)
$5.83
>>> print(d1-d2)
$-3.43
>>> price = Dollar(0.99)
>>> 'The price is {}'.format(price)
'The price is $0.99'

Do you see the difference? ;)

Also there is alot more, but for the beginning is that enough.