An average league game takes about ~32-34 minutes on average.
Assuming about half of the games you play are lost, and half are won, the average earned IP from each game is ~79 ip.
There are 131 champions;
13 cost 450
21 cost 1350
24 cost 3150
41 cost 4800
32 cost 6300
32*6300+ 41*4800+ 24* 3150 + 21*1350 + 13*450 = 508200 total IP cost needed
Assuming a player plays 3 games a day on average he will earn 3*79 + 150(win of the day) = 387 ip/day
508200/387 = 1313+ days needed at 3 games a day to get all league champions, or 3.5 years.
For the record, this doesn't include rune pages and runes themselves. For each rune page you want to get, you'll have about half a month or 48 games, if you want full runes on that rune page it'll cost you probably between 4k-12k more, depending on what you buy. So that's another 50+ games, or over a month.
Of course, if you want to have 6 rune pages with runes, it would mean 6 months of playing 3 games every day.
Not to mention that in these 4 years you spend grinding, Riot would have released many more champions, further delaying the process.
I don't understand why anyone would think this is acceptable at all. We need to speak up so Riot will do something about these outrageous costs. It shouldn't take me 3-5 years to grind champions and runes.