I am looking to make a full runepage for him as he is my favorite champ. Which are the best ones to buy?

move speed. armor, magic pen, and magic resist.

just to clarify cardboardowl's post -

quints - movement speed
reds - magic pen
yellows - armor
blues - flat or scaling magic resist

Just because Singed is awesome.

MS Quints, But I used AP until I could afford them
Mpen Reds, nothing else you can really put there
Armor yellows
Blues- Scaling MR does wonders. AP / Ap scaling if you want singed damage O.o

Move speed quints are really important. All of the pages above are good, but I really want to stress the MS quints to you. Save up and buy those first, they are almost required for Singed as he needs to be fast.

Can I buy a full rune page of top tier runes for 6000 ip?

No, its more expensive

I use armor reds personally.

Look up a singed guide on Solomid, it will also tell you the prices of runes.

MS Quints are 2050 each (X3=6150)
all the other runes can be bought for 205 each (x27= 5535)

So you're looking at over 10K IP for a full runepage for anyone.

If you're looking to get a rune page that you can use on more champs, go Marks of Insight, Seals of Resilience, Glyphs of Shielding and either Quints of Mobility (Movement speed 2050 each) or Quints of Potency (1025 each). These will be useful on almost any AP champ.

If you're on a budget

Flat Armor Yellows and MR/lvl Blues are the most versatile runes in the game- there isn't a champion out there that they aren't good on. Jungling REQUIRES flat armor runes.

Reds- magic pen is standard for all casters. Worth getting.

Quints- I use MS quints on every champion except supports, for which I run g/10

So, these are runes that are generic, good on just about everyone, and well worth picking up for not just singed, but for most of the champions in the game.