This week is a bit disapointing to me. The only expensive champion, Kog'maw, is one of the two expensive champions I have unlocked.
I have only been playing this game for around 2 months, but I am pretty sure some of these guys (amumu, soraka, ect.) are free for their 3rd time since I have started. It seems like Riot mainly just rotates 450 and 1350 IP champions, with new champions and maybe one expensive champion every other week.
I find it a little disapointing. When I started playing I had thought that the free weekly rotation was a thing that gave you a chance to play all the campions now and then, not the just cheap ones.