Arthur Bishop's 'girlfriend' was really a high class hooker
That was a strange scene revolving around professional hitman, Arthur Bishop, visiting his ostensible girlfriend, who is never named in the movie, but played by Bronson's real-life wife actress, Jill Ireland.
In the morning when Bishop is almost dressed and ready to go, his girlfriend rolls over and tells Bishop that it will cost one hundred dollars more for the letter she wrote for him. Then we see what's reality. The blonde is a high class prostitute of which Bishop is a regular client. Bishop can only pretend to live a 'normal' life outside of his real occupation. Bishop still harbors a deep-seated psychological need, existent in all of us, to be a normal man with normal desires such as having a girlfriend to visit, socialize, and make love. Bishop is no longer able to do that but he satisfies this need by enlisting the paid services of a high class hooker who is willing to perform men's fantasies, if the money is right. But in the end, a hooker is still a mercenary. More services cost more money. Bishop makes money hand over fist terminating high-value human targets, so the extra one hundred is nothing as he really did like the make-pretend, love letter. Don't forget that in 1972, one hundred dollars is equivalent to several days pay for a minimum wage laborer, about a week, give or take.