I've been playing with Ahri for the past few days (she is on the free-to-play rotation this week), and I really like the way she plays. Currently, she costs 6300IP which may not seem like a lot to players who've been playing for a long time and have accumulated a great deal of IP, but in my case that is a lot. I'm just below seven-thousand IP, but I just want to know if there is a schedule of any kind for sales.
In short: is there any way for me to tell if Ahri (or other champions) will go on sale? or am I better off just buying her instead of holding my breath?
I know that older champions get cheaper over time, but I'm not sure when Ahri was released. Also I looked at this, but I feel as though it doesn't address what I'm looking for.
Note: I'm only spending with IP not RP.