Can't print out a string with $ in it

Question

I was quite bored and decided to experiment by making my own string 'encoder'. Everything went fine until I noticed a 'error' I'd say.

In the code I have two functions encode & decode, then argparse. The whole code pretty much looks like this:

def decode(thestring):
    decoded = ""
    for letter in thestring:
        if (letter == '~'):
            decoded += str('A')
        elif (letter == 'K'):
            decoded += str('a')
        elif (letter == '2'):
            decoded += str('B')
        elif (letter == 'n'):
            decoded += str('b')

Tried using '$' as some pages suggested, but not much of a luck. Also tried using '$$' and I got an output, but not what I expected.

elif (str(letter) == 'r'):
    encoded += str('$')

.

elif (str(letter) == 'r'):
    encoded += str('$$')

https://i.stack.imgur.com/t7nFc.png (without '$$') https://i.stack.imgur.com/5VD4l.png (with '$$')

I'm trying to make the $ dollar sign to work in a string and then to be able print it out after 'encoding' and 'decoding' Anyone could help me with a solution to this..?