All the other friendlies have been £10 for a terrace only ticket if you order online before the game. Just go online and print out your ticket. Or I think you can just show it on your phone. Easy enough if you know you want to go beforehand.
On the night if you turn up ticketless it'll cost more and you have to queue up at the ticket office. Frankly I think it's a pain in the backside for people to do it that way but there you go.
No need to get in a fluster about it though.
As for prices for the league games this seems to be a big mystery. Your guess is as good as mine.