I'm confused by Champion prices...

Me and a friend who started about the same time were discussing champs and both decided to buy the same one.

We both had 2k~2.1k IP, I was waiting because it told me the champ costs 3150 but my friend told me it costs only 1350 for him. At first I thought he was being dyslexic and reading the numbers wrong, but then he showed me that he had bought it. Meanwhile I'm sitting there staring at the 3150 and when I try to buy it I am told "Not enough RP/IP".

... what gives? O_o

How can the exact same champ have different prices for two different people? Is this normal? o_O