Katarina costs 6300 IP to buy at the moment instead of 3150. In addition, her RP prices is 975 instead of 790.

Additional Notes:
Ezreal costs 6300IP/975 RP as well despite being reduced to 4800 IP/880 RP
Caitlyn as well.
Evelynn costs 6300 IP/975 RP instead of 1350 IP/585 RP

The prices don't get updated on the PBE like they do for the Live servers. Probably not worth their time coding it since we get free RP/IP anyway.

Ahh, okay, I see. Just thought it was kind of weird seeing as Katarina has never been 6300 IP (as far as I could remember)

Not 100% positive on this but I am pretty sure Riot is doing this because you get free RP and IP as 6k IP is not a lot in that matter.

-Best of luck, Google