Ticket prices anounced by the club. £35/£42/£45 for adults depending on your seat. Plus Athens is £5 to £8 less.
In my case (OAP) I've saved £25 by buying the bundle. Had I waited and purchased only two games it would have cost £70 or £65 which is cheaper than the £75 I paid.
It will be difficult for the club in that they sold the tickets very cheap (note that UEFA rules state away tickets fixed at 45 euros). I'd imagine ticket prices will be £40+ for these games but if you paid £100 for three games I think they have every right to offer you £20 for an unused ticket.