You can always extend a logical line across multiple physical lines with parentheses:
answer = (
'Ten for that? You must be mad!' if does_not_haggle(brian)
else "It's worth ten if it's worth a shekel.")
This is called implicit line joining.
The above uses the PEP8 everything-indented-one-step-more style (called a hanging indent). You can also indent extra lines to match the opening parenthesis:
answer = ('Ten for that? You must be mad!' if does_not_haggle(brian)
else "It's worth ten if it's worth a shekel.")
but this leaves you hitting the 80-column maximum all the faster.
Where precisely you put the if and else portions is up to you; I used my personal preference above, but there is no specific style for the operator that anyone agrees on, yet.