There is no booking fee for PM's. What there is though is a big confusion of DL agents. Sometimes when they don't know what they are doing they cannot price an AF segment correctly on DL (especially the feeder flights to CDG when you're connecting) and put you in full Y. That is what bloats the fares past being ridiculous (like $5k for Economy).

One very talkative agent was communicating every step to me once: when she tried to book CDG-ATH she first tried it with a DL-coded flight number and there were issues, the price bloating from $1.5k to over 4k. She then looked that very same segment up under its AF-code and, voilá, back to $1,5k for the entire trip.