Rune prices vary significantly--in fact, some of the best runes are also the cheapest.
First of all, there is little reason to get Tier 1 and tier 2 runes--tier 1 runes give little to no stats, while tier 2 runes are terribly cost-inefficient compared to tier 3 runes. You want full sets of tier 3 runes because while, say, +0.95 AD marks may not look like much on their own, having 9 of them will set you significantly ahead early game (you can last hit much easier, trade harass better, etc.)
It might be a bit too late, but usually we recommend to start saving IP for tier 3 runes at summoner level 15... it's a fact of life that runes tend to be awfully expensive, unfortunately. :/ that can't be helped though.
Here are my recommendations for first runes to buy:
1. Flat armor seals (yellows). These are only 205 IP each (relatively cheap, I guess), and I believe having all 9 gives you like an extra 13 armor or so early game--pretty much the best runes in the game imo. A must have for jungling, and a godsend against strong physical enemies early.
2. magic resist/level glyphs (blues). These are also only 205 IP each, and really help a lot late game vs powerful ability power mages. An AD carry who only has 30 MR late game is a sad panda when he or she gets instabursted by a fed AP carry
3. If you play AD, get flat armor pen or AD marks (reds). If you play AP, get flat magic pen marks (reds). I think these are all 410 IP each, but AD really helps out your early game last hitting and damage trading, and AP really helps out your early game spells (mpen runes + sorc shoes against an opponent with no mr = close to true damage).
4. For quints, I'd recommend flat AD or armor pen for AD champions, and flat AP for AP champions. If you want one set of quints for everyone, try flat movespeed.
P.S. Usually around Christmas, Riot has an IP sale on arpen, mpen, movespeed, and flat hp quintessences--try picking up the movespeed quints then if it happens this year.
Hope this helps!