I played over 3500 normal games an ~1500 - ranked games in total since I started playing league 4 years ago and I still don't have all champion, that is mostly because I don't want some of them and waste my IP on name changing or something.
To get the IP to afford a 6300 IP champ, you have to play roughly 60 games.
This might seem much at first, but once you really get into the game, that's nothing, really.
Buying a champion for so much ip should still the need of another new champion for a while, untill then, you should have enough ip again.
You can play the champs in rotation to try our a diversity of champions and decide then which champion might interest you.
To the point of higher IP cost champion being SO MUCH BETTER, that is not true.
Annie costs 450 IP and is one very easy to play champ and yet extremely strong when playing right of course.
High IP cost champion often have weird mechanics that have to be learned first and are harder.