I rode it this year...
There is no cost of entry, but accommodation can be expensive if you chose to use it.
This year, Matt sorted us out a good rate at the hostel in Banff before the start. On the first day of the race, I had a serious tyre splitting problem and had to stay in a hotel for $100. It's cheaper once you get to America, though. Some places know about the race and will go as low as $35/night. You can also share with other riders if circumstances allow.
Food costs are higher than you might think for the US. Remember the places you can buy food are pretty rural so charge a lot more than you would expect in a normal city.
Bike costs depend on your luck. I think I spent about $130 in Steamboat to change a couple of things: new rear tyre, new (SS) drivetrain.
Really, you want to take the financial side out of the equation once you've started. It costs what it costs, and if you need a hotel to dry your gear you'll just want to get one.
I'm a vegetarian and didn't have any trouble getting food. Most people don't carry cooking equipment anyway so it will only affect you in restaurants and in avoiding gelatin. On the bike, I ate loads of sugary crap. At restaurants, I enjoyed big fat American breakfasts.
The vegan fixie girl took absolutely ages (31 days) to finish. It's an impressive feat that she made it, but I wouldn't say she "raced" it.
I have a US Visa because I also made a (failed) attempt on the PCT. I think the normal method (Visa waiver) only allows you to stay for 30 days. Depending on your plans, that might not be enough.
I think the most realistic account of the race is The Story of Eight.
I enjoyed the film before I did the race but it doesn't accurately portray what it is like. First off, Mary would have been disqualified under current rules for having external encouragement and for travelling along the route in the car when she temporarily gave up. Also, it makes the riding look quite boring - the vast majority is non-technical but not as boring as the film looks. The whole "spiritual journey" thing isn't necessarily applicable. It wasn't for me - it was a great ride, but not a life-changing event.