For those who are unaware, this is how the new price reduction schedule works:
New champion launch price is 7800 IP / 975 RP.
After one week, the price is reduced to 6300 IP / 975 RP.
Each release, the oldest 6300 is reduced to 4800 IP / 880 RP.
Each third release, an additional 4800 IP or lower champion is reduced to one of the remaining tiers: 3150 IP / 790 RP, 1350 IP / 585 RP, or 450 IP / 260 RP
When we see the release of the next champion, who has been confirmed to be female and was teased in the Pool Party promotional image, Xerath will be reduced to 4800 IP / 880 RP and Miss Fortune will be reduced to 3150 IP / 790 RP.
For the champion after that we'll see Graves reduced to 4800 IP / 880 RP. And after that one - so we're talking three champions away now - Shyvana will be reduced to 4800 IP / 880 RP.