Ever wondered what Flexiplus is? As you approach the terminal, you see the signs - essentially it's a way of getting on the train whenever it suits you.
The usual deal is that you book a crossing for (let's say) 1230. But suppose you don't know what time you are going to be getting back (maybe you are driving up from the south of France in peak holiday season). With a regular ticket, if you are early, you wait; if you are late, they try to put you on a train with spaces, but maybe you wait a long time.
Pay for a Flexiplus ticket, though, and you get on the first train that suits you. There's a dedicated check in, a private lounge and priority boarding. You still have to go through the big delayer though - UK Border Control.
The private lounge is nice - one late evening they must have decided to give us a free upgrade, and directed us through the Flexiplus channel. The lounge had a very nice premium coffee machine - help yourself, no extra charge. The loo was nice, and you didn't have to trek across the car park to get to it. And a nice lady gave us a little picnic hamper.
So how much? It varies, depending on the usual supply and demand, but it's roughly an extra hundred quid. Is that worth it?
For me, it's rare that I would benefit. Outbound I usually set off after work and get there pretty late on when all the queues have gone. Homeward bound, coming from a village fairly close to the Channel, I usually arrive close to my scheduled departure time anyway, so it's no big deal.
But maybe - if I was that guy trekking across France, not sure what time I was going to get to Calais, car full of screaming kids, then £100 to get on the first train and miss the bank holiday crowds, - yes, I would be tempted.