3150 - akali, gangplank, gragas, karthus, shen, twitch
4800 - ahri, brand, ezreal, graves, jarvan, kennen, lee, leona, malzahar, nocturne, renekton, riven, shyvanna,  vayne,  xerath
https://support.riotgames.com/hc/en-us/articles/202083304-Permanent-Champion-Price-Reduction#top
add changes if anyone comes after rek'sai

not on purchase list:
450 - ashe, yi, poppy, sivir
1350 - cho, fiddles, jax, malph, nasus, teemo, trynd
3150 - kassadin, leblanc, mordekaiser, olaf, ramnus, shaco, urgot
4800 - caitlyn, cass, galio, kog, maokai, rumble, sejuani, skarner, swain, talon, viktor, vlad, voli, wukong, yorick