As you probably remember, Tobar told you that you would have to pay him ~400 bottlecaps each time you plan on using his ferry. Thankfully you can resolve this situation by performing a few simple tasks. Make sure that you've talked to Catherine even before you've used the boat for the first time (more on that in the Prologue section). Once you've arrived in Point Lookout you'll have to find Catherine's daughter named Nadine. She can be found easily while trying to complete the third main quest. All you have to do is to visit the Ark & Dove Cathedral and talk to her. Agree to meet Nadine near the Point Lookout Pier after talking to her about the person who has taken a part of your brain.
You should be greeted by Nadine after you get to the pier [#89]. It would be wise to ask her a few questions during this conversation concerning the ritual from the swamps and the person who's taken a part of your brain. Nadine will tell you that Tobar is the one responsible and that she's been able to trap him in the Engine Room. You can now go and meet him by opening the left door.
A new conversation will automatically begin when you get to the Engine Room. You can talk to Tobar and ask him why he's doing this to find out that he's collecting trophies or you can you choose a response that will trigger a fight. Perform a quick execution on Tobar and examine his body to collect a few useful items. The most precious find can be found on a table to your right [#90]. It's going to be the missing piece of your brain. :-)
You can now travel between Point Lookout and Capitol Wasteland freely, because you won't be forced to buy tickets anymore. Each time you plan on leaving one area go to a small room and use the bed. When you return to Capitol Wasteland after dealing with Tobar don't forget to talk to Catherine. She should be standing somewhere close to the ferry [#91] assuming it's safe. The woman will reward you for finding Nadine with 300 bottlecaps and 10 Punga fruits.